Notes  on  Heating 
and  Ventilation 


NOTES 

•  O    ~ 


ON 


r\ 


HEATING  and  VENTILATION 


BY 


JOHN  R.  ALLEN 

J| 

PROFESSOR  MECHANICAL  ENGINEERING 
University  of  Michigan 

Member  American  Society  Heating  and 
Ventilating  Engineers 

Member  American  Society  Mechanical 
, .  I          .  4  .  Engineers 

Member  American  Society  Promotion 
Engineering  Education 


THIRD 


DOMESTIC  ENGINEERING  COMPANYI 

CHICAGO 

443  So.  DEARBORN  STREET 
1911 


COPYRIGHT 

DOMESTIC    ENGINEERING    CO. 
191  1 


t> 


TABLE  OF  CONTENTS. 

Introduction. 

Theory  of  heat  and  measurement  of  tempera- 
ture    1 

Chapter  I. 

Heat  losses  from  buildings  and  rules  for  deter- 
mining the  heat-losses  in  different  construc- 
tions   7 

Chapter  II. 

Different  forms  of  heating  systems;  their  ad- 
vantages, disadvantages  and  relative  economy.  28 

Chapter  III. 

The  design  of  a  direct  steam-heating  system  and 
the  properties  of  steam;  steam-tables;  loss  of 
heat  from  radiators;  rules  for  direct  heating..  38 

Chapter  IV. 

Design  and  installation  of  an  indirect  steam- 
heating  system;  rules  for  indirect  heating....  65 

Chapter  V. 

Steam-boilers  and  steam-piping.  Determination 
of  size  and  details  of  construction 76 

Chapter  VI. 

,The  connection  of  mains  to  risers  and  risers  to 
radiators,  with  illustrations  of  different  ar- 
rangements in  practical  use;  steam-piping, 
piping  systems,  size  of  return-mains,  valves 
and  piping-connections 82 

Chapter  VII. 

The  design  of  a  hot-water  heating  system;  radi- 
ator heat-losses,  rules  for  direct  and  indirect 
system 120 

i 

241307 


Chapter  VIII. 

Hot-water  boilers  "and  piping.  Determination 
of  size"  and  details  of  construction  t y . . .«.  127 

Chapter  IX. 

Ventilation  and  pollution  of  air  by  human  be- 
ings, artificial  lighting  and  chemical  processes; 

systems  of  ventilation >;'. ....;....:  .141 

?  i 
Chapter  X. 

Design  of  hot-air  heating  systems,  construction 
and  rules  .....: 152 

Chapter  XI. 

Fan  system  of  heating,  with  tables  of  fan  capac- 
ities and  condensation  in  heater-coil;  air^mix- 
ing  systems 164 

Chapter  XII. 

A  central  heating  system;  its  (Jesign  and  instal- 
lation; witli*  discussion  of  different  methods 
of  carrying  pipes  underground;  specific  ap- 
paratus; combination  system  of  steam  and  hot 
water :  l . .  .• • .187 

Chapter  XIII. 

/"*•  t     '*  .'        „  ~ 

Pipe  coverings,  pipe,  air-valves  and  fittings 209 

Ctiar/ter  XIV,  * 

Auxiliary  devices  TO?"  heating  systems,  regula- 
tion of  humidity -rand  draft;  air-washers  and 
vacuum-heating  systems  . .  /. 218 


SUBJECT  INDEX 


Page 


Air    change,    ordinary    as- 
sumption for 146 

changes  necessary   144 

dilution  143 

inlets  and  outlets 148 

mixing  systems   182 

piping   system    220 

pollution    tests    142 

quantity  to  be  supplied.  166 

valves   202,  212 

valves,    pitch    and    sup- 
port of  pipes 139 

washers  223 

Anchors  and  hangers 201 


B 


Boiler  horse-power    80 

Boilers   188 

fire   tube    76 

hot-water   127 

proportion  of 78 

steam   76 

water  tube  . ,  .76 


Carbon  dioxide 144 

Central  heating  systems..  187 

Chemical  processes 143 

Circuits,  multiple  and 

single  129 

Coils,  heating  172 

Cold-air  duct  155 

Combination  of  heating 

systems  36 

Combination  system  87 

Combustion,  products  of..  142 

Conduction  10 

Connections  of  radiators.  109 
Connection  to  mains  and 

risers  99 

Convection  .  .  13 


Page 

Convection,  losses,  calcula- 
tion of   13 

Covering  for  pipes 209 


Damper  regulators  221 

Dams    83 

Determination  of  building 

heat-loss  21 

Direct   and   indirect   com- 
binations     73 

Direct  heating,  rules  for . .   55 
Direct  hot-water  heating.   22 

Direct  steam-heating 32 

Disc   fans    184 

Drainage,  pipe   94 

Drip  connections  101 

Duct,    cold-air    155 


Economy  of  different  sys- 
tems      36 

Expansion  joints  •  97 

Expansion  of  pipes 96 

Expansion  tank  129 


Factors  for  exposure 21 

Fan-heating  systems  ....104 
Fan,  size,  speed  and 

horse-power  K7 

Fan  system  of  heating 34 

Fittings  '...217 

Fittings,  resistance  of.... 137 

Flow  mains  and  risers 128 

Flow,  velocity  of 136 

Flue  proportion,  hot-air. .  .157 

radiators  50,  75 

Flues,  foul  air 157 

hot-air  156 

materials  of 184 

Furnaces,  hot-air  153 


Page 

Furnaces,    hot-air,    opera- 
tion of    .  159 


Grate    surface,    proportion 

of    79 

Grates    28 

Gravity  system 90 

Gravity  systems    189 


Hangers  and  anchors 201 

Heat    1 

Heat  generated  by  human 

beings 143 

Heat  generated  by  illumi- 
nation   144 

Heat-loss      for      buildings 

determined 21 

Heat-loss  from  building..     7 
Heat-loss     from     indirect 

steam  radiators  65 

Heaters,  cast-iron 176 

Heating    and    power    sys- 
tem, combination  of 191 

Heating  apparatus,  classi- 
fication of 28 

Heating  systems,  auxiliary 

devices  for   218 

High  -pressure  systems. . . .  190 

Hot-air   furnaces 30,  153 

furnaces,   operation  of.  .159 

leaders  and  flues 156 

pipe,  size  of 73 

system 152 

system  rules   160 

systems,  proportions  of.  158 
Hot-water  boilers  and 

piping 127 

direct 32 

heating  indirect 34 

heating  rules    124 

heating  system 120 

piping    128 

Humidity  regulations   221 


Indirect   heating   rules 71 

hot-water  heating   34 


Page 

hot-water  radiators   122 

radiators,  heating  effect 

of   70 

radiators,  installation  of  68 

steam  heat  losses 65 

steam-heating  33 

steam-heating  design...   65 
Insulation   .  ...195 


Joints,   expansion 


Leaders,   hot-air   156 

Legs  of  the  system 129 

Loss   of  heat   from   build- 
ings   14 

Low-pressure  pump  return 
system    191 


M 


Mains     82 

and  risers,  location  of..  99 

size  of  steam  return...  91 

steam,  rules  for  sizes  of  92 

Materials,  specific  heat  in     3 

Measurement    of    work...     2 

Moisture-supply  to  heated 

air    154 

Multiple  circuit  system...  129 


One-pipe  system   85 

Open  and  closed  circuits.  .134 
Overhead  distribution....  89 
Overhead  system  132 


Paints   for  radiators,   val- 
ues of   53 

Pipe 216 

and    fittings,    resistance 

of    137 

covering    209 

drainage    94 


Page 

expansion    96 

sizes    138,  199 

supports  119 

Pipes,    method    of    carry- 
ing   194 

Pipes,  pitch  and  support..  139 

Piping,    hot-water    128 

steam    82 

systems     84,  129 

Pitch    83,  129 

Power    and    heating    sys- 
tems combined 191 


Radiation    8 

Radiator  connections    109 

heat-losses    121 

installation     53 

sizes    47 

Radiators,    different   types 
of  relative  efficiency. .   44 

flue  50,  75 

heat  loss  under  varying 

temperatures     51 

indirect  hot- water   122 

loss  of  heat  from 42 

Relation  between  heat  and 

work    2 

Reliefs  or  drips 82 

Resistance     of     pipe     and 

fittings    137 

Respiration,   products  of..  142 

Return   82 

mains  and  risers 128 

mains,   sizes  of  steam..   91 

system,  pump  191 

Risers 82 

Risers  and  mains,  location 

of 99 

Rules    for   determining 
heat-losses    22 


S 


Single  circuit  system 131 

Single-pipe    system    135 

Siphon     83 

Specific  heat  3 

Steam  and  hot-water  sys- 
tems  combined    206 

heating  direct   ,.   32 


Page 

indirect    33 

nature  and  properties  of  38 

piping 82 

system  indirect  design..  65 

Stoves    30 

Supporting  of  pipes 119 


Tables    

air   dilution    143 

air-pollution  tests 142 

capacity  of  mains 138 

capacity  of  risers 139 

condensation  and  heat 
given  off  by  heater- 
coils  173 

condensation   chart    177 

conduction  power  10 

dimensions      and      heat 

losses    57 

disc-fan  efficiency    183 

fan  capacities  168 

fan  efficiency    169 

fans,  disc    184 

heat  given  off  by  illumi- 

nants   144 

heat-loss  from  flue  radi- 
ators    50 

heat-losses  from  indi- 
rect radiators  67 

heat-transmission   52 

heat- transmission  for 

varying  pressures 211 

heater  dimensions    176 

hot-air  figuring   161 

indirect  hot-water  radi- 
ators   124 

indirect  radiators — tem- 
peratures of  leaving 

air    68 

loss  from  wrought  iron- 
pipe  and  cast-iron 

radiators   42 

pipe-size  practice   93 

pollution  by  lighting.  ...143 

properties  of  steam 40 

proportion    of    cast-iron 

hot-water  boilers   129 

proportions     of     hot-air 

heating  systems    159 

pressure  losses  ..  ..181 


Page 

radiating  power 9 

radiator  tappings   54 

rate  of  transmission 121 

rating  of   house-heating 

boilers    80 

relative   effectiveness   of 
different      thicknesses 

of  covering  210 

relative    size    of    steam 

and  return  main 94 

relative  temperatures  of 

air  and  room 63 

relative  value  of  differ- 
ent pipe  coverings.  ..  .210 
relative  value   of  radia- 
tor paints  53 

results    of    computation, 

direct  system   58 

results  of  computations, 

indirect  system    72 

results  of  computations, 

direct   hot- water 125 

size  of  hot-water  mains.137 
size  of  flues  for  indirect 

radiators    70 

specific  heats    3 

specific  heat  of  gases...     6 
speeds,     capacities     and 
horse-powers  of  single 
inlet,    fans   at   various 

pressures   171 

steam    39 

temperature  chart   178 

temperatures  assumed  in 

heating    25 

values  of  air-conditions.   17 

values  of  E 18 

values  of  K 20 

values    of    material    and 
surface 18 


Page 

values     of     temperature 

difference    18 

velocity      of     hot-water 

circulation    137 

wrought   iron    and    steel 
steam,   gas  and  water 

pipe   215 

Tank,  expansion   129 

Temperature    1 

Temperature  regulation . . .  219 

Thermostat,  Johnson  219 

Transmission  of  heat  un- 
der various  conditions..  64 

Traps,   steam    84 

Tunnels    for    steam    sys- 
tems     197 

Two-pipe   systems 86 


Unit  of  heat. 


Vacuum  heating  systems. 225 

Valves 98,  217 

Valves,  air  139 

Velocity  of  flow 13£ 

Ventilating  ducts    177 

Ventilation 141 

Ventilation,   effects  of 

poor   147 

Ventilation    systems    147 


W 


Water-hammer 
Water-line  .... 
Water-seal  .... 


vi 


PREFACE 


THE  subject  matter  originally  contained  in  this 
book  was  a  reprint  from  a  series  of  articles  pub- 
lished in  Domestic  Engineering.  In  this  edi- 
tion the  original  text  has  been  rewritten  and  a  large 
amount  of  additional  information  included. 

This  book  was  written  primarily  to  show  that  the 
subject  of  Heating  and  Ventilation  could  be  developed 
in  a  logical  way  from  the  fundamental  principles  of  en- 
gineering. The  great  lack  has  been  in  the  amount 
of  scientific  information  available  regarding  the  actual 
laws  of  heat  and  the  value  of  the  constants  entering 
into  these  laws.  The  University  of  Michigan  has  car- 
ried on,  under  the  direction  of  M.  E.  Cooley,  Dean  of 
the  Engineering  Department,  a  series  of  experiments 
for  over  twenty  years.  The  results  of  these  experi- 
ments are  given  in  various  tables  and  serve  to  give  the 
designer  data  from  actual  experiments  upon  which  he 
can  base  his  calculations. 

There  has  been  included  in  this  edition  a  resume  of 
the  results  of  the  German  experiments  and  these  meth- 
ods of  determining  heat  losses  from  buildings.  This 
matter  is  largely  reprints  from  a  book  published  by 
the  "Metal  Worker"  under  the  title,  "Formulae  and 
Tables  for  Heating"  by  J.  H.  Kinealy.  This  book  has 
been  written  primarily  for  the  steamfitter  and  designer 
of  heating  systems.  It  presupposes  some  elementary 
knowledge  of  the  details  of  construction  and  opera- 
tion of  the  simpler  forms  of  heating  plants. 

The  author  has  used  the  previous  editions  as  a  text 
for  his  classes  in  Heating  and  Ventilation.  The  pres- 
ent edition  has  been  written  with  a  view  to  making 
the  book  more  desirable  as  a  college  text. 

July  1,  1911.  John  R.  Allen. 


INTRODUCTION 


Heat. — Heat  is  a  form  of  motion.  In  modern  sci- 
ence, all  matter  is  conceived  as  being  made  up  of 
small  particles  called  molecules.  These  particles  do 
not  exist  in  a  state  of  rest,  but  are  in  constant  vibra- 
tion. If  these  particles  move  slowly  the  body  is  at  a 
low  temperature;  if  they  move  more  rapidly  the  body 
is  at  a  higher  temperature,  the  temperature  of  the 
body  being  determined  by  the  rapidity  of  the  motion 
of  the  particles.  In  measuring  heat  there  are  two 
properties  to  be  considered — the  intensity  and  the 
quantity.  This  may  be  compared  to  measuring  water 
in  a  pipe.  We  measure  the  pressure  of  the  water  in 
the  pipe  by  means  of  a  gauge  in  pounds  per  square 
inch.  The  quantity  of  water  is  measured  in  pounds. 
In  the  same  way  the  intensity  of  heat  is  measured  by 
the  thermometer  in  degrees  and  the  quantity  of  heat  is 
measured  by  comparison  with  the  quantity  of  heat 
which  a  pound  of  water  will  absorb. 

Temperature. — Temperature,  which  is  a  measure  of 
the  intensity  of  the  heat  of  a  body,  might  also  be  con- 
sidered as  measuring  the  velocity  of  the  molecules  of 
the  body.  In  mechanical  engineering  all  measure- 
ments of  temperature  are  made  on  the  Fahrenheit 
scale.  On  this  scale  the  freezing  point  is  taken  at  32° 
and  the  boiling  point  as  212°,  the  tube  of  the  ther- 
mometer between  these  points  being  divided  into  180 
equal  parts  called  degrees. 

We  never  know  the  total  amount  of  heat  in  a  body. 


Notes         on          Heating         and         Ventilation 

As  it  is  impossible  to  bring  any  body  to  a  condition 
of  absolutely  no  heat,  the  heat  in  any  body  must  al- 
ways be  measured  from  some  assumed  zero  point  and 
in  the  Fahrenheit  scale  this  assumed  zero  point  is  32° 
below  the  freezing  point.  For  theoretical  purposes, 
however,  it  is  highly  desirable  to  have  some  absolute 
standard  of  heat.  A  perfect  gas  at  32°  contracts  about 
1/493  of  its  volume  for  each  degree  Fahrenheit  that  it 
is  reduced  in  temperature.  If,  then,  we  keep  on  de- 
creasing the  temperature  of  a  perfect  gas  from  32°, 
until  it  reaches  a  point  493°  below  32°  Fahrenheit,  it 
would  have,  theoretically,  no  volume.  If  it  has  no 
volume,  the  amount  of  heat  which  it  contains  must  be 
zero.  This  point,  then,  is  called  the  absolute  zero. 
This  point  is  manifestly  an  ideal  one.  To  find  the 
absolute  temperature  in  degrees  it  is  necessary  to 
add  to  the  Fahrenheit  temperature  461  degrees,  that 
is,  32°  Fahrenheit  corresponds  to  493°  absolute. 

Unit  of  Heat. — Heat  is  not  a  substance  and  it  can 
not  be  measured  as  we  would  measure  water  in  pounds 
or  cubic  feet,  but  it  must  be  measured  by  the  effect 
which  it  produces.  Suppose  it  requires  a  certain 
amount  of  heat  to  raise  a  pound  of  water  from  39°  to 
40°  Fahrenheit.  It  would  require  three  times  that 
quantity  of  heat  to  raise  a  pound  of  water  from  39°  to 
4&°  Fahrenheit.  The  heat  required  to  raise  a  pound 
of  water  one  degree  Fahrenheit  is  called  a  British 
thermal  unit,  and  is  designated  by  letters  B.  t.  u. 

Relation  Between  Heat  and  Work. — Work  is  meas- 
ured in  foot-pounds.  The  unit  of  work  is  the  work 
required  to  raise  one  pound  through  a  height  of  one 
foot.  Ten  units  of  work  or  ten  foot-pounds  would  be 
the  amount  of  work  done  in  raising  ten  pounds  one  foot 
high  or  one  pound  ten  feet  high.  Heat  is  a  form  of 
motion,  hence  there  must  be  some  definite  relation  be- 

2 


Notes         on         Heating         and         Ventilation 

tween  heat  and  work.  This  relation  was  first  deter- 
mined by  Joule.  By  a  series  of  experiments  Joule  found 
that  one  heat  unit  was  equivalent  to  778  foot-pounds. 
It  is  possible,  then,  to  express  heat  either  in  heat  units 
or  in  foot-pounds. 

Specific  Heat. — Different    substances    require    very 
different  quantities  of  heat  to  produce  the  same  change 
of  temperature  for  the  same  weight.    As  for  example, 
to  raise  one  pound  of  water  one  degree  requires  one 
B.  t.  u. ;  to  raise  one  pound  of  ice  one  degree  requires 
.504  B.  t.  u. ;  to  raise  one  pound  of  wrought  iron  one 
degree  requires  1138  B.  t.  u.     The  heat  necessary  to\ 
raise  one  pound  of  a  substance  one  degree,  expressed   j 
in  British  thermal  units,  is  called  specific  heat.     They 
following  table  gives  the  specific  heat  of  the  principal 
substances  which  we  meet  with  in  engineering  work: 

TABLE  I.     SPECIFIC  HEATS. 
Substance.  B.  t.  u. 

Liquids. 

Water    1.000 

Alcohol    622 

Turpentine    472 

Petroleum    434 

Olive   Oil    309 

Metals. 

Cast  iron   1298 

Wrought   iron 1138 

Soft   steel    1165 

Copper  0951 

Brass   0939 

Tin 0569 

Lead 0314 

Aluminum    2185 

Minerals. 

Coal 2777 

Marble     - 2159 

Chalk   2149 

Stones   generally    ". 2100 

Limestone   2170 

Building  Materials. 

Brick    work    1950 

Masonry    2159 

Plaster  2000 

Pine    wood    467 

Oak  wood    570 

Birch     480 

Glass    1977 

3 


Notes         on         Heating         and         Ventilation 

Example. — It  is  required  to  raise  the  temperature  of 
a  cast  iron  radiator  weighing  300  pounds  from  70°  to 
212°.  The  temperature  through  which  the  iron  would 
be  raised  would  then  be  212  minus  70°  or  142°.  From 
the  table  we  see  that  it  would  require  to  raise  one 
pound  of  cast  iron  one  degree  .1298  heat  units,  then  to 
raise  one  pound  142°  would  require  142  times  .1298  or 
18.43  heat  units,  and  to  raise  300  pounds  one  degree 
would  require  300  times  this  amount  or  5,529  B.  t. 
u.,  the  heat  required  to  heat  the  radiator.  This  is 
important  in  heating  as  the  walls  of  a  cold  building 
must  be  heated. 

Example. — A  church  80'xlOO'  with  walls  2y»  feet 
thick  for  10  feet  above  the  ground  and  for  the  re- 
maining 20  feet  2  feet  thick.  The  roof  has  a  y-2  pitch 
and  is  made  of  2"x8"  rafters,  16  inches  on  centers, 
covered  with  1  inch  of  pine  boarding,  tar  paper  and 
slate  y^  inch  thick.  Main  floor  composed  of  two  1-inch 
thicknesses  of  boards  laid  on  2"xl2"  joists,  16-inch 
centers.  Ceiling  is  of  plaster  yi  in  thick.  The  church 
has  20  windows,  6  feet  wide  and  15  feet  high,  12  win- 
dows, 4  feet  wide  and  6  feet  high,  and  2  doors,  8  feet 
wide  and  12  feet  high.  Allowing  an  addition  of  15% 
of  furnishings,  find  the  heat  required  to  raise  the  tem- 
perature of  the  church  from  0°  to  50°. 

Weight  of  stonework,  stone  weighing  160  pounds 
per  cubic  foot. 

370x10x2^x160=1,480,000  pounds 
v5l68x20x2     x!60=2,350,000 

soT  q 

— x40x2x2     x!60--=l,024,000         "      '] 
2 


Total  weight  of  masonry  assuming  ) 
building  to  be  without  openings  I 


Notes         on         Heating         and         Ventilation 


Weight  of  wood  work.     Weight  per  cubic  foot  taken  as  40 
pounds. 
2x8 

x56. 2x75x2x40.=  37,600  pounds  of  rafters. 

144 
56.2x104x2x1/12x40=  39,000  pounds  of  roof  boards. 

80x100x2x2/12x40=107,600  pounds  of  joists        > 
2x12  • 
— x80x75x2x40...=  80,000  pounds  of  floor   boards       ' 
144                   ,  • 
Total  weight  of  wood- 
work  263,600  pounds. 

Slate — Weight  per  cubic  foot  taken  as  170  pounds. 

56.5x104x2x1/48x170=41,600    pounds. 
Plaster — Weight  per  cubic  foot  taken  as  90  pounds. 
(360x30x80x40^-100x80)  %xl/12x90=124,000  pounds. 
Air — Weight  per  cubic  foot  taken  as  .08  pounds. 
80 

(80x30x100-) x40xlOO)  .08=32,000  pounds. 

Heat  required.  2 

4, 854, 000x50x.2159=52, 300,000  B.  t.  u. 

263,600x50x.65     =  8,580,000  B.  t.  u. 

41,600x50x.2159=      448,000  B.  t.  u. 

124,000x50x.2       =  1,240,000  B.  t.  u. 

32,000x50x.2375=      379,000  B.  t.  u. 


62,947,000  B.  t.  u. 

Adding    15%    for    furnishing =  9,440,000  B.  t.  u. 

Total  to  raise  building  and  fur-     - 

nishing    50    degrees =72,389,000  B.  t.  u. 

This  item  is  a  large  one  in  determining  the  size  of 
the  heating  plant  to  be  installed  in  a  building  inter- 
mittently heated. 

In  solid  substances  the  change  in  volume  when  they 
are  heated  is  so  small  that  it  is  not  considered.  In 
gases,  however,  the  change  in  volume  when  the  gas  is 
heated  without  being  confined,  depends  directly  upon 
the  absolute  temperature  and  may  be  very  large. 
When  air  is  confined  and  is  heated,  it  cannot  expand ; 
if  it  does  not  expand  there  is  no  work  done  because, 
from  our  definition  of  work,  it  is  necessary  when  work 
is  done,  that  the  body  have  some  movement.  On  -the 
other  hand,  when  air  receives  heat  and  is  free  to  ex- 
pand it  does  work.  For  instance,  if  air  w,ere  confined 
in  a  cylinder  by  a  piston,  and  this  air  were  heated,  the 
air  would  expand  and  the  piston  would  be  moved  out. 

5 


Notes         on         Heating         and         Ventilation 

As  the  piston  is  moved  through  a  certain  space  there 
must  be  work  done.  On  the  other  hand,  if  the  piston 
were  blocked  so  that  it  could  not  move,  then  the  air  on 
being  heated  would  do  no  work.  Then  in  these  two 
cases  different  amounts  of  heat  will  be  required  to 
raise  the  substance  one  degree,  depending  upon 
whether  there  is  external  work  done  or  not.  It  is  nec- 
essary then  in  gases  that  we  consider  two  specific 
heats,  the  specific  heat  of  constant  volume  and  the  spe- 
cific heat  of  constant  pressure.  For  air  the  specific 
heat  of  constant  volume  is  .1689,  for  constant  pressure 
it  is  .2375.  It  is  seldom  that  we  use  air  in  a  confined 
space,  so  that,  so  far  as  this  work  is  concerned,  we 
shall  in  most  cases  consider  the  specific  heat  of  air  as 
.2375 — that  is,  to  raise  one  pound  of  air  one  degree 
requires  .2375  B.  t.  u.,  the  pressure  being  constant. 

TABLE  IA.     SPECIFIC  HEATS  OF  GASES. 

Constant  Constant 

Substance.                                                          Pressure.  Volume. 

Air     2375  .1689 

Oxygen     2175  .1550 

Hydrogen     3.4090  2.4122 

Nitrogen    2438  .1727 

Steam   5000  .3500 

Carbonic  Acid   Coa 2479  .1758 

Ammonia  .                 508  .299 


Notes  on  Heating  and  Ventilation 


CHAPTER  I 

Heat  Loss  from  Buildings. — Heat  is  lost  from  a  room 
in  three  ways — by  the  direct  transmission  of  the  heat 
through  the  walls  and  windows ;  by  the  passage  of  air 
up  the  foul-air  flues,  and  by  the  nitration  of  air  through 
the  walls  and  air  leakage  around  doors  and  windows. 
The  first  two  losses  are  easily  determined,  but  the  de- 
termination of  the  loss  by  filtration  must  always  in- 
volve a  large  factor  of  judgment  and  experience. 

All  building  construction  is  more  or  less  porous. 
This  is  well  exemplified  by  the  old  experiment  made 
with  a  common  brick.  Two  cornucopias  of  paper  are 
pasted  on  opposite  sides  of  a  common  brick,  the  large 
end  of  the  cornucopias  being  fastened  to  the  brick.  Op- 
posite the  small  end  of  the  cornucopia  at  one  side  is 
placed  a  lighted  candle.  By  blowing  into  the  cornucopia 
on  the  opposite  side,  the  candle  may  be  blown  out,  the 
air  having  passed  directly  through  the  brick. 

The  experiments  which  have  been  made  in  order  to 
determine  the  loss  generally  tend  to  show  that  in  the 
ordinary  well-constructed  building  the  air  in  the  room 
will  change  about  once  per  hour,  when  all  doors  and 
windows  are  closed. 

In  order  to  study  the  other  heat  losses  from  a  room 
it  will  be  necessary  to  study  the  laws  of  cooling.  A 
body  may  be  cooled  in  three  different  ways — by  radia- 
tion, by  conduction  and  by  convection  (contact  of 


Notes 


on          Heating          and          Ventilation 


air).     In  order  to  understand  these  losses  more  thor- 
oughly, each  will  be  considered  separately. 

Radiation. — The  heat  that  passes  from  a  body  by 
radiation  may  be  considered  similar  to  the  light  which 
is  given  off  by  a  lamp.  There  is  always  a  transfer  of 
radiant  heat  from  the  body  of  a  higher  temperature  to 
the  body  of  lower  temperature.  The  amount  of  heat 

7///////////////A 


60° 
J 


W 


I 

X 


Air  60' 


Fig.   1. 

radiated  will  depend  upon  the  difference  in  tempera- 
ture between  the  bodies  and  the  substance  through 
which  this  heat  passes  and  the  material  composing  the 
surface  from  which  the  heat  is  radiated. 

The  losses  by  radiation  may  be  better  understood  by 
referring  to  Fig.  1.     Suppose  the  plate  PP  to  be  of 

8 


Notes          on          Heating         and         Ventilation 

cast  iron  1  foot  square  and  1  inch  thick.  Let  us  sup- 
pose this  plate  to  be  on  both  sides  at  a  temperature 
of  60°.  Let  this  plate  form  one  side  of  a  room,  the 
walls  WWW  being  non-conducting  substances  and  at 
a  temperature  of  59°,  the  air  in  this  space  being  at  a 
temperature  of  60°.  Since  the  plate  and  the  air  in 
the  space  are  at  the  same  temperature,  there  will  be 
no  loss  of  heat  from  the  air  to  the  walls,  but  all  the 
heat  that  passes  from  the  plate  PP  to  the  walls  must 
pass  by  radiation.  For  ordinary  temperatures  of  heat- 
ing surfaces,  say  60  or  70°,  the  loss  by  radiation  will 
equal  the  difference  in  temperature  between  the  hot 
body  and  the  cold  body  multiplied  by  a  factor  repre- 
senting the  radiating  power  of  the  body.  The  follow- 
ing table  gives  the  radiating  power  of  different  sub- 
stances : 

TABLE   II.      RADIATING  POWER. 

Radiating  power  of  bodies,  expressed  in  heat  units,  given  off  per 
square  foot  per  hour  for  a  difference  of  one  degree  Fahrenheit. 
(Peclet.) 

Copper,  polished   0327 

Iron,    sheet    0920 

Glass    595 

Cast    iron,    rusted 648 

Building  stone,   plaster,  wood,   brick 7358 

Woolen  stuffs,   any  color 7522 

Water    1.085 

Heat  is  radiated  in  straight  lines  exactly  as  light  is 
given  off  from  the  source  of  light.  We  may  have  heat 
shadows  the  same  as  we  have  light  shadows  and  the 
intensity  of  the  heat  is  inversely  proportional  to  the 
square  of  the  distance  from  the  source.  Some  bodies 
are  transparent  to  heat  and  other  bodies  absorb  heat, 
the  same  as  some  bodies  are  transparent  to  light  and 
others  absorb  light.  The  transparency  of  bodies  to 
heat  is  called  diathermancy.  Gases,  such  as  air,  oxy- 
gen, nitrogen,  and  hydrogen,  are  almost  perfectly 

9 


Notes         on         Heating         and         Ventilation 

transparent  to  heat,  while  wood,  hair,  felt  and  other 
non-conducting  bodies  are  almost  perfectly  opaque  to 
the  transmission  of  heat.  The  loss  of  heat  by  radia- 
tion is  independent  of  the  form  of  a  body  so  long  as  it 
does  not  radiate  heat  to  itself.  The  color  or  condition 
of  the  surface  of  different  bodies  affects  their  radiant 
power.  Smoothly  polished  surfaces  radiate  less  heat 
than  rough  surfaces.  As,  for  instance,  a  surface  painted 
with  lamp  black  will  radiate  over  13  times  as  much 
heat  as  a  polished  copper  surface. 

Example. — Suppose  we  have  a  glass  surface  five 
square  feet  in  area.  The  glass  surface  is  at  a  tempera- 
ture of  70°  and  the  objects  surrounding  it  are  at  a 
temperature  of  zero.  From  the  table  we  see  that  one 
square  foot  of  glass  (surface)  loses  .595  heat  units  in 
an  bour  for  a  difference  of  one  decree  between  it  and 
the  surrounding  objects.  For  a  difference  of  70°,  then, 
each  square  foot  -of  glass  would  lose  70  times  that 
amount,  or  41.5  heat  units,  and  5  square  feet  of  glass 
would  lose  5  times  that  amount,  or  207.5  heat  units  per 
hour  by  radiation  only. 

Conduction. — The  heat  transmitted  by  conduction  is 
the  heat  which  is  transmitted  through  the  body  itself. 

TABLE    III.      CONDUCTING    POWER. 

The  conducting  power  of  materials,  expressed  in  the  quantity  of 
heat  units  transmitted  per  square  foot  per  hour  by  a  plate  one 
inch  thick,  the  surfaces  on  the  two  sides  of  the  plate  differing  in 
temperature  by  one  degree.  (Peclet.) 

B.  t.  u. 

Copper     515 

Iron     233 

Lead     , 113 

Stone 16.7 

Glass     6.6 

Brick  work   5.6 

Plaster     3.7 

Pine  wood   76 

Sheep's   wool    .323 

10 


Notes         on         Heating         and         Ventilation 

For  example,  take  the  condition  shown  in  Fig.  2.  PP 
is  a  plate,  one  side  of  which  is  enclosed  by  the  walls 
WW.  Let  the  temperature  of  the  plate  outside  be  59°, 
the  temperature  on  the  inside  of  the  plate  be  60°  ;  the 
temperature  of  the  walls  be  60°,  and  the  temperature 
of  the  air  in  the  room  be  60°.  Then  all  the  heat  that 


ear 


Air  6(T 


60" 


W6O 


Fig.   2. 


is  lost  by  the  room  must  be  lost  by  direct  conduction 
through  the  plate.  PP.  The  amount  of  heat  conducted 
will  depend  upon  the  material  of  which  the  conductor 
is  composed  and  in  addition  it  will  also  depend  upon 
the  difference  in  temperature  between  the  two  sides  of 
the  plate  and  upon  the  thickness  of  the  plate.  The 

11 


Notes 


o  n 


Heating          and          Ventilation 


conduction  through  any  plate  may  be  calculated  as  fol- 
lows: 

Multiply  the  factor  given  in  Table  III  by  the 
difference  in  temperature  between  the  two  sides  of  the 
plate  and  divide  the  result  by  the  thickness  of  the  plate 
in  inches.  The  quotient  will  be  the  heat  transmitted 
by  conduction  per  square  foot  of  surface. 


60" 
S' 


'////////////^///////^^^^^ 

W  60' 

I 


60* 


i     Air  59* 


W 
60° 


m?%%^^ 

Fig.  3. 

Example. — Suppose  a  Boiler  plate  5  feet  square,  1A- 
inch  thick,  to  have  a  temperature  of  70°  on  one  side 
and  a  temperature  on  the  opposite  of  200°.  The  dif- 
ference in  temperature  of  the  two  sides  of  the  plate 
would  be  130°.  The  amount  of  heat  conducted  would 
then  be  233  X  130  -4-  y2  =  15,145  B.  t.  u.  per  square 

13 


Notes         on          Heating         and         Ventilation 

foot  of  plate  per  hour.  Then  five  square  feet  would 
transmit  five  times  this  amount,  or  75,725  B.  t.  u.  in 
one  hour. 

Convection. — Loss  by  convection  is  sometimes 
termed  loss  by  contact  of  air.  Take,  for  example,  the 
condition  shown  in  Fig.  3.  Let  P  be  a  vertical  plane 
of  metal  one  foot  square,  having  its  surfaces  main- 
tained at  60°  temperature.  Let  the  walls  WW  also  be 
at  a  temperature  of  60°.  Let  the  air  in  the  room  be 
59°.  In  this  case  there  will  be  no  loss  of  heat  from 
the  walls  to  the  plate  by  radiation  and  there  will  be 
no  loss  through  the  plate  by  conduction,  but  heat  will 
be  transmitted  from  the  walls  and  the  plate  to  the  air 
of  the  room.  The  air  which  comes  in  contact  with  the 
warmer  walls  will  be  heated.  As  air  is  heated  it  be- 
comes lighter  and  rises  and  a  current  is  formed.  This 
produces  a  circulation  of  air,  and  this  circulation  of 
air  gives  rise  to  a  loss  of  heat  by  convection  or  contact 
of  air. 

The  loss  of  heat  by  convection  is  independent  of  the 
nature  of  the  surface,  wood,  stone  or  iron  losing  the 
same  quantity  of  heat,  but  it  is  affected  by  the  form  of 
the  body — that  is,  a  cylinder  and  a  sphere  would  lose 
different  amounts  of  heat  per  square  foot.  Take  the 
steam  radiator,  for  example.  The  air  nearest  the  radi- 
ator becomes  heated  and  rises;  as  it  rises  its  place  is 
taken  by  other  colder  air  coming  off  the  floor  so  that 
a  current  of  air  is  established.  In  the  ordinary  type 
of  radiator,  the  loss  by  contact  of  air  represents  about 
half  the  loss  of  heat,  the  balance  being  loss  by  radia- 
tion. 

Calculation  of  Convection  Losses. — The  calculation 
of  the  heat  lost  by  convection  is  quite  complicated  and 

13 


Notes         on         Heating         and         Ventilation 

different  expressions  have  been  derived  for  this  loss  for 
different  forms  of  surfaces.  Those  developed  by  Peclet 
are  given  in  Box's  treatise  on  Heat. 

The  rules  given  for  convection  in  the  text-books  on 
heat  cannot,  as  a  rule,  be  applied  to  the  loss  of  heat 
from  buildings.  All  these  rules  assume  that  the  air 
surrounding  the  object  is  in  a  perfectly  quiescent  state. 
In  buildings  this  is  not  the  case,  for  the  air  surround- 
ing a  building  is  rapidly  circulated  by  the  winds.  The- 
oretically a  high  building  would  lose  proportionally 
less  heat  than  a  low  building,  because  in  the  upper 
stones  there  would  be  a  smaller  difference  in  temper- 
ature between  the  air  inside  the  room  and  the  air  out- 
side than  in  the  lower  stories.  This,  however,  is  not 
the  case,  as  the  wind  circulates  the  air  outside  the 
building  and  makes  the  temperature  of  the  air  sur- 
rounding the  building  on  the  outside  practically  the 
same  at  all  levels. 

Inside  the  room,  however,  the  air  at  the  top  of  the 
room  is  much  warmer  than  that  at  the  floor.  The  re- 
sult is  that  the  rate  of  transmission  of  heat  in  rooms 
with  high  ceilings  is  appreciably  higher  than  in  rooms 
with  low  ceilings,  as  in  the  room  with  a  high  ceiling 
we  have  a  greater  difference  of  temperature  between 
the  inside  and  the  outside  air  at  the  ceiling.  This  dif- 
ference is  not  ordinarily  considered  unless  the  height 
of  the  room  exceeds  ten  feet.  If  the  height  of  the  room 
does  not  exceed  ten  feet  the  temperature  taken  five 
feet  above  the  floor  line  may  be  assumed  as  the  average 
temperature  of  the  room. 

The  loss  of  heat  from  buildings  was  first  investi- 
gated both  experimentally  and  theoretically  by  Peclet. 
The  greater  part  of  his  work  is  given  in  Box's  treatise 

14 


Notes          on          Heating          and          Ventilation 

on  Heat.  The  results  obtained  by  Peclet  are  difficult 
to  apply  practically  and  nearly  all  the  rules  that  are 
used  to  determine  the  loss  of  heat  from  a  building  are 
largely  empirical.  The  constants  determined  by  the 
German  government  are  probably  the  most  reliable 
we  have. 

The  German  formulas  and  tables  were  translated  by 
J.  H.  Kinealy  and  published  under  the  title  "Formu- 
las and  Tables  for  Heating,"  by  the  "Metal  Worker/' 
The  following  pages  outline  the  German  method  as 
given  in  the  pamphlet  mentioned. 

In  the  simplest  form  of  building  the  walls  consist 
of  one  solid  piece  of  the  same  material  and  in  this 
case  the  transmission  of  heat  is  from  the  air  of  the 
room  to  the  wall  by  convection,  through  the  wall  by 
conduction  and  from  the  surface  of  the  wall  to  the  cold 
air  outside  by  convection.  Such  a  wall  is  shown  in 
Fig.  4. 

A  solid  wall  may  be  made  up  of  a  series  of  layers 
of  different  materials,  as  shown  in  Fig.  5.  The  trans- 
mission of  heat,  however,  goes  on  in  the  same  way. 

In  a  wall  such  as  is  shown  in  Fig.  6,  the  heat  passes 
through  each  of  the  consecutive  walls  just  as  it  does 
through  a  solid  wall.  Heat  always  passes  from  a 
warmer  to  a  colder  body.  Hence  t/,  the  temperature 
of  the  inside  of  the  wall,  must  be  less  than  the  tem- 
perature of  the  room  t,  and  the  temperature  t0'  must 
be  greater  than  the  temperature  of  the  outside  of  the 
wall  t0'.  Each  particle  in  a  section  of  the  wall  must 
have  a  different  temperature,  the  temperature  dimin- 
ishing as  the  particle  is  nearer  and  nearer  to  the  out- 
side wall. 

The  quantity  of  heat  transmitted  through  a  given 
area  of  wall  must  be  the  same  for  each  point  in  the  sec- 

15 


Notes 


on 


Heating         and         Ventilation 


tion  when  the  wall  has  once  reached  a  stable  condition. 
The  quantity  of  heat  which  passes  per  hour  from  the 
warm  air  of  the  room  to  a  square  foot  of  wall  will  be 
in  Figs.  4,  5  and  6  ax  (tj — t/),  and  the  heat  which 
passes  from  the  outside  wall  to  the  cold  outside  air  is 
a0  (t0' — 10).  If  the  wall  has  an  air  space  as  in  Fig.  6, 
the  heat  which  passes  to  the  air  space  will  be  a/(t2' — 


F/6 


F/G. 


t2),  and  the  heat  given  by  the  air  space  to  the  outer 
wall  will  be  a/  (t2—  t2"). 
The  heat  that  passes  through  the  wall  by  conduc- 

tion, as  stated  before,  will  be  in  Fig.  4  -'-  (t/  —  t/), 


and  in  Fig.  6  for  the  inner  wall—  (t/  —  t/),  and  for 

Xi 

the  outer  wall  ~-  (t2"  —  1</).     If  the  layers  of  this  wall 

are  of  similar  material,  e±  and  e2  will  be  equal. 

In  order  to  use  these  expressions  it  is  necessary  to 
know  the  temperature  of  the  wall  surface.  These  tem- 
peratures are  not  known.  The  only  known  temperatures 
are  the  temperature  of  the  air  inside  the  room  and  the 
air  outside  the  building.  Let  us  assume  that  the  heat 


Notes          on          Heating         and          Ventilation 

transmission  through  the  wall  may  be  represented  by 
the  expression  k  (tx — 10),  where  k  is  a  constant  to  be 
determined. 

The   amount  of  heat  passing  through   the  wall   at 
each  point  is  constant,  hence  we  have  for  Fig.  4: 

K  (ti—  t0)=a1(tl—  t,')=aB(V—  t0)  =  —  (t/— to')  (1) 

x 

and  for  Fig.  6 : 

K  (tt—  t0)=a1(ti—  ti')=a/(V—  t.,)=a2'(t2—  t,")=a0(t0'— 10) 

— (t!'— 12')=—  (t2"— to')   (2) 

Xi  X2 

Solving  for  k  in  equation  (1) 

K  = (3) 


and  in  equation  (2) 

i 

K  =  —  -(4) 

11  1  1        X,       X2 

—+— +—+—+— +  — 

ai     ai'    a2'    a0     61      e2 

For  thin  glass  or  thin  metal  walls,  —is  a  very  small 
quantity  and  may  be  neglected. 

The  values  of  a  and  e  must  be  known  before  k  can 
be  determined.  The  value  of  the  convection  factor, 
a,  is  determined  by  Grashof  by  the  following  equation : 

(40  c  +  30d)  T 

a  — -  c  -f  d  H 

10,000 

c  as  a  factor  depends  on  the  condition  of  the  air, 
whether  at  rest  or  in  motion.  Rietschel  gives  the  fol- 
lowing values  for  c : 

TABLE  IV.     VALUES  OF  c. 

e. 

Air  at  rest,  air  in  rooms 82 

Air  with  slow  motion,  air  in  rooms  in  contact  with  windows..  1.03 
Air  with  quick  motion,  air  outside  of  a  building 1.23 

17 


Notes         on         Heating 


and 


Ventilation 


d  is  a  factor  depending  upon  the  material  compos- 
ing the  wall  and  on  the  condition  of  the  surface.  The 
values  for  d  may  be  taken  as  follows : 

TABLE   V.      VALUES   OP  d. 


Substance.  d. 

Brickwork    74 

Mortar  and  similar  materials    .74 

Wood 74 

Glass 60 

Cast    iron    65 

Paper     78 


Substance.  d. 

Sheet  iron    57 

Sheet    iron    polished 092 

Brass    polished    053 

Copper     033 

Tin    045 

Zinc     .  .049 


T  is  the  difference  between  the  temperature  of  air 
and  that  of  the  surface  of  the  wall.  For  poor  con- 
ductors or  very  thick  walls  it  may  be  taken  as  zero. 


te 


r/cj 

In    approximate    calculations    it    is    usually   taken    as 
zero.    The  following  values  of  T  are  given  by  Rietschel : 

TABLE  VI.      VALUES   OF  T. 

Brick  work    5  inches  thick 14.4 

Brick  work  10  inches  thick 12.6 

Brick  work  15  inches  thick ,. . .  10.8 

Brick  work  20  inches  thick >. .  9.0 

Brick  work  25  inches  thick 7.2 

Brick  work  30  inches  thick 5.4 

Brick  work  40  inches  thick 1.8 

For   single   windows 36. 

For  double  windows 18. 

For  wooden  doors 1.8 

Table  VII  gives  values  of  e.     These  values  vary 
considerably  for  different  authors. 

TABLE  VIT.     VALUES  FOR  e. 

e. 

Brick  work   5.6 

Mortar,  plaster   •. 5.6 

Rubble  masonry 14. 

18 


Notes         on         Heating         and         Ventilation 


Limestone    ....................................................     15. 

Marble,  fine  grained  ...........................................     28. 

Marble,    coarse    grained  .......................................     22. 

Oak  across   the   grain  ......................  ...................       1.71 

Pine,    with    the    grain  .........................................       1.4 

Pine,    across    the    grain  ........................................  76 

Sandstone    ....................................................     10. 

Glass    .........................................................       6.6 

Paper  ..........................................................  27 

For  example,  assume  a  brick  wall  as  shown  in  Fig- 
ure 7.  There  are  four  air  contact  surfaces  and  two 
walls  through  which  conduction  takes  place,  then  : 

K  is  the  same  as  in  equation  4. 

Rietschel  assumes  a/,  a2"  and  a0'  equal  and  he  uses 
the  same  value  of  T  as  for  a  solid  of  thickness  equal 
to  the  brick  work  without  the  air  space. 

(40X.8?+30X.74)10 


10,000 
(40X1.^34-30X74)10 

=2.04 
10,000 

Since  both  walls  are  of  brick  work 
Xl       4.75 
—  =  --  =  .85 
e,        5.6 
X2       8.25 

-1.47 
e          5.6 
Substituting  in  equation  (5) 

1 
k  -  =.214 

.62-f.62+.6k-|-.49-f.  85-|-1.47 
Making  this  same  calculation,  neglecting  T  gives 
k  =.210 

19 


Notes         on         Heating         and         Ventilation 


The  following  values  of  k  have  been  determined  by 
using  equations  (3)  and  (4)  as  shown  in  the  example. 


TABLE    VIII.      VALUES    OF  k   ADOPTED   BY   PRUSSIA. 


Brink  work.  k. 

4.72    inches  thick... 492 

9.85    inches  thick 348 

inches  thick..  .266 


Masonry,    sandstone. 


k. 


15 

20.1 

25.2 

30.2 

35 

40.5 

45.6 


inches    thick 226 

inches   thick 184 

inches    thick 164 


11.8  inches  thick 451 

15.7  inches  thick 39 

19.7  inches  thick 348 

23.8  inches  thick 318 

27.6  inches  thick 287 

31.6  inches  thick..  .266 


inches    thick 133      35.4    inches    thick 246 


inches    thick .123 

inches   thick 113 


39.4    inches    thick 226 

43.3    inches    thick 205 

47.2   inches   thick 195 

For  limestone  masonry  the  values  of  k  should  be 
taken  10%  larger  than  those  given  for  sandstone. 

TABLE  IX. 

Values  of  k  for  various  forms  of  brick  walls.     Brick  are  assumed 
8*4x4x2,  laid  with   %-inch  mortar  joints.     Plastering  %  of  an  inch 

Outside  Walls.  Inside  Walls. 

Plaster 


Thickness 
of  Wall. 


brick 


4% 


No 

Plaster, 
k 

.52 
.37 
.29 
.25 
.22 
.19 
.16 
.14 
.12 


One  Side 
Plastered. 

k 

.49 

.36 

.28 

.24 

.21 

.18 

.16 

.14 

.12 


One  S'ide 
Plastered 
and  2.4  Air 
Spaces  in 
the  Wall, 
k 

.25 
.21 
.19 
.16 
.14 
.13 
.12 

Board 
and  Air 
Space  Be- 
tween Wall 
and  Board, 
k 
.29 
.24 
.21 
.20 

Plas- 
tered 
Both 
Sides. 
k 

.43 

.33 

.  6 


For  doors,  wooden  walls  and  windows,  the  values  of 
k  are  given  in  Tables  X,  XI  and  XII. 


TABLE  X.  DOOR  OR  WOODEN  WALLS. 


Thickness — 


Pine    — 

Inside.          Outside. 


Oak    

Inside.        Outside. 


^  inch    

%  inch    

1  inch   ,... 

1*4  inch   

1%  inch   31 

2  inch    26 


k 

.52 

.44 

.39 

.34 


k 
.56 
.47 
.41 
.36 
.32 
.27 


k 

.64 
.59 
.54 
.50 
.47 
.41 


k 

.70 

.ea 

.58 
.54 
.50 
.43 


TABLE   XI.      WINDOWS'  AND  WALLS. 

Single  window 1.03 

Single  window,   double   glass 62 

Double  window 46 

20 


Notes         on          Heating         and         Ventilation 

Single  skylight  .  1.16 

Double  skylight  48 

Stud  partition,  lath  and  plaster  one  side 60 

Stud  partition,  lath  and  plaster  both  sides 34 

Lath  and  plaster  ceiling  space  above  unheated 62 

Floor  %  inch  thick,  cold  space  below 45 

Floor  %  inch  thick,  lath  and  plaster  on  under  side,  cold  space 

below  26 

Floor  double  1%  inches  thick,  cold  space  below 31 

Floor  double  iy2  inches  thick,  lath  and  plaster  on  under  side, 

cold  space  below 18 

TABLE  XII.     OUTSIDE  WALLS. 
Walls  having  lath  and  plaster  on  the  inside,  and  outside  is  covered 

as  described. 
Outside  covering —  k. 

Overlapping  clapboard  7-16  inch  thick „...     .44 

Paper  and  clapboards 31 

%    inch   sheathing  and  clapboards 28 

%  inch  sheathing,  paper  and  clapboards 25 

Factors  for  Exposure. — The  heat  losses  given  in  the 
tables  should  be  increased  as  follows:  Where  the 
room  has  a  north  or  northwestern  exposure  and  the 
winds  are  severe,  add  20  to  30  per  cent.  When  the 
building  is  heated  in  the  day  time  only  and  allowed 
to  cool  during  the  night,  add  20  per  cent.  When  the 
building  is  heated  occasionally — for  example,  a 
church — add  from  40  to  50  per  cent.  Where  a  room 
has  a  northerly  exposure  and  is  subjected  to  extremely 
high  winds,  add  30  per  cent.  It  is  usually  advisable 
to  assume  for  unwarmed  spaces,  such  as  cellars  and 
attics,  a  temperature  of  about  32°.  For  vestibules  and 
entrances  unheated,  which  are  being  frequently  opened 
to  the  outer  air,  a  temperature  of  20°  may  be  assumed. 

Determination  of  the  Loss  of  Heat  from  a  Build- 
ing.— In  determining  the  loss  of  heat  from  a  building 
all  surfaces  should  be  considered  which  have  on  the 
outside  a  lower  temperature  than  the  temperature  in 
the  room.  If  a  room  is  situated  over  a  portion  of  the 
cellar  which  is  not  heated,  the  loss  of  heat  through 
the  floor  should  be  considered.  If  the  room  has  over 
it  an  unheated  attic  the  loss  through  the  ceiling  should 

21 


Notes         on         Heating         and         Ventilation 

be  considered.  In  most  cases  where  the  attic  has  no 
window  it  is  warm  enough  so  that  the  heat  loss 
through  the  ceiling  may  be  neglected.  The  loss 
through  the  sides  of  a  room  which  is  surrounded  by 
rooms  at  the  same  temperature  may  be  neglected. 
Doors  entering  directly  into  a  room  from  outside  are 
roughly  considered  to  lose  the  same  amount  of  heat  per 
square  foot  as  windows. 

Rules  for  Determining  the  Loss  of  Heat. — A  com- 
mon rule  for  the  loss  of  heat  from  a  building  is  that 
given  by  Professor  R.  C.  Carpenter  in  his  book  on 
"Heating  and  Ventilation."  This  rule  is  developed 
from  the  following  consideration :  Referring  to  Table 
IV,  we  notice  that  one  square  foot  of  glass  conducts 
approximately  four  times  as  much  heat  as  a  brick 
wall  20  inches  thick.  If,  then,  we  divide  the  wall  sur- 
face by  4,  the  result  will  give  us  the  number  of  square 
feet  of  glass  surface,  which  would  lose  the  same  quan- 
tity of  heat.  Adding  to  this  the  actual  glass  surface 
would  give  us  the  total  equivalent  glass  surface.  In 
addition  to  this  heat  transmitted  through  the  walls  we 
must  add  the  heat  which  is  lost  by  the  air  which 
passes  directly  through  the  walls  themselves.  It  is 
assumed  that  for  ordinary  sized  rooms  the  air  in  the 
room  will  be  changed  about  once  an  hour,  so  that 
we  must  figure  on  heating  the  entire  air  in  the  room 
about  once  per  hour.  One  cubic  foot  of  air  weighs, 
approximately,  1/13  of  a  pound.  To  raise  a  pound 
of  air  one  degree  requires  .238  B.  t.  u.  Then  to 
raise  one  cubic  foot  of  air  one  degree  would  require 
.238  X  1/13  =  .0183  B.  t.  u.  or  one  heat  unit  will  heat 
l-f-.0183:=54.6  cubic  feet,  or  in  round  numbers  say  55. 
If,  then,  we  divide  the  contents  of  a  room  by  55  we 


Notes          on          Heating         and         Ventilation 

will  have  the  heat  lost  by  filtration  through  the  walls. 
Adding  these  factors  together  will  give  the  total  heat 
lost  from  the  room.  This  rule  may  be  expressed  more 
concisely  as  follows : 

RULE  1. — Divide  the  contents  of  the  room  by  55;  add 
the  glass  surface  and  add  to  this  sum  the  zvall  surface  di- 
vided by  4.  The  sum  urill  be  the  heap  lost  from  the  room 
per  degree  difference  of  temperature  between  the  air  in 
the  room  and  the  air  outside  the  room.  Multiply  this 
sum  by  the  difference  in  temperature  between  the  air  in- 
side the  room  and  that  outside  of  the  room  and  the 
product  will  be  the  heat  lost  from  the  room. 

This  rule  can  be  expressed  algebraically  as  follows: 
Left  C  represent  the  volume  of  the  room,  W  the  wall 
surface,  G  the  glass  surface  and  d  the  difference  of  tem- 
perature between  the  air  outside  and  the  air  inside  the 
room.    The  heat  loss  from  the  room  per  hour  expressed 

f    Cn  W  ] 

in  B.  t.  u.'s  zvould  be   J  -          -)-          --\-G\-d,  ivherc  n 

[     55  4  J 

is  a  factor  which  depends  upon  the  tightness  of  the  room 
and  varies  in  value  from  I — 3.  For  ordinary  room  «=1, 
for  corridors  1.5,  for  vestibules  2  to  3. 

It  is  quite  customary  to  assume  the  difference  in 
temperature  between  the  air  in  a  room  and  the  air 
outsjde  to  be  70°.  Where  the  windows  are  poorly 
fitted  or  the  house  loosely  built  the  loss  by  filtration 
should  be  doubled,  and  in  halls  where  the  doors  are 
being  opened  and  closed  frequently  this  should  be 
multiplied  by  three. 

There  is  one  criticism  on  this  method  of  figuring 
the  heat  loss  in  the  room.  The  diffusion  loss  is  as- 
sumed to  depend  upon  the  cubic  contents  of  the  room, 

83 


Notes         on          Heating         and         Ventilation 

This  of  course  is  manifestly  not  correct,  as  the  diffu- 
sion loss  occurs  through  the  walls  and  windows  and 
must  depend  upon  the  area  of  the  walls  and  windows. 
The  rule,  however,  will  work  very  well  for  rooms  of 
average  size,  but  where  the  rooms  have  excessive  wall 
and  window  surfaces,  or  where  the  cubic  contents  of 
the  room  is  large  compared  to  the  wall  and  window 
surfaces,  this  rule  will  give  inconsistent  results.  The 
following  rule  seems  to  the  author  to  be  capable  of  a 
much  wider  application: 

RULE  2. — Divide  the  wall  surface  by  4;  add  the  glass 
surface;  multiply  this  sum  by  the  difference  in  tempera- 
ture between  the  air  in  the  room  and  the  air  outside,  and 
then  multiply  the  result  by  ll/2.  This  rule  is  for  a  well 
constructed  building.  If  the  building  is  old  and  poorly 
built  then  instead  of  multiplying  by  1l/2  the  result  should 
be  multiplied  by  2;  entrance  halls  multiplied  by  2l/2. 
This  rule  may  be  expressed  algebraically  as  follows : 
Let  W  represent  the  wall  surface,  G  the  glass  surface, 
and  d  the  difference  of  temperature  between  the  air  out- 
side and  the  air  inside  the  room.  Then  the  heat  loss 
from  the  room  per  hour  expressed  in  B.  t.  u.'s  would 

{  w      \ 

\je  J 1_  G  rd  n,  where  n  is  a  factor  which  depends 

I     * 

upon  the  construction  of  the  house  or  location  of'  the 
room  and  varies  in  value  from  1.5  to  2.5,  as  stated  above. 

In  figuring  the  radiating  surface  for  any  room  the 
cubic  contents  should  always  be  taken  into  consideration. 
In  a  large  room  with  a  small  exposed  wall  surface,  if 
only  enough  radiation  is  put  in  to  cover  the  loss  from 
walls  and  windows,  the  room  will  be  slow  to  heat.  In 
to  taking  care  of  the  loss  from  walls  and  win- 

84 


Notes         on         Heating         and         Ventilation 

dows  it  is  necessary  for  the  radiator  to  heat  the  air  in 
the  room  itself.  In  order  to  do  this  a  large  proportion 
of  this  air  must  either  pass  through  the  heating  device 
or  be  carried  out  by  the  ventilating  flues,  so  that  where 
the  cubic  contents  of  a  room  is  large  it  is  advisable  to 
add  from  10  to  20  per  cent  to  the  radiating  surface  to 
allow  for  the  heating  of  the  air  in  the  room  itself.  The 
above  remark  applies  only  when  the  building  is  inter- 
mittently heated ;  when  the  building  is  continuously 
heated  it  is  not  necessary  to  consider  the  volume  of  the 
room. 

The  following  temperatures  are  usually  assumed  in 
determining  the  heat  losses : 

TABLE  XIII.      TEMPERATURES  ASSUMED  IN  HEATING. 

Degrees. 

Temperature  of  stores 68 

Temperature  of  residences 70 

Temperature  of  halls  and  auditoriums 64 

Temperature  of  prisons   65 

Temperature  of  factories 60  to  68 

Temperature   of   cellars   not   warmed 32 

Temperature  of  outside  entrances 20 

Temperature  of  attics  not  warmed " 32 

The  average  temperature  for  the  period  of  the  year 
during  which  buildings  are  heated  throughout  the  Cen- 
States  may  be  assumed  to  be  approximately  35°. 

The  following  examples  will  show  the  method  to  be 
pursued  in  determining  the  heat  lost  from  a  building: 

EXAMPLE  1. — Suppose  a  room,  as  shown  in  Fig. 
8.  Let  the  temperature  be  maintained  in  the  room  at 
70  degrees,  the  temperature  of  the  outside  air  be  0.  Let 
the  walls  be  of  brick,  8  inches  thick,  plastered  on  plaster 
board  on  the  inside,  the  windows  be  2^x6  feet,  the  ceil- 
ing of  the  room  be  10  feet  high.  Let  the  room  be  on 
the  second  floor  of  the  building,  the  rooms  above  and 
below  heated.  The  window  surfaces  are  ^ 

85 


Notes          on          Heating          and          Ventilation 


square  feet.  The  total  wall  surface  is  £0x10=200  square 
feet.  The  net  wall  surface  is  200 — 30=170  square  teet. 
Then  the  heat  lost  from  the  room  per  degree  difference 

70' 


o" 


70" 


70' 


Fig.    8. 

of  temperature  by  rule  2  would  be  170-f-H-30=72^. 
As  the  difference  between  the  outside  and  inside  tem- 
perature is  70°,  the  total  heat  lost  is  72^x70=5,075 
B.  t.  u.  per  hour. 

26 


Notes         on         Heating         and         Ventilation 

Example  2. — Take  the  same  room  as  Example  1, 
except  that  the  room  is  covered  by  a  flat  tin  roof. 
The  air  space  between  the  ceiling  of  the  room  and 
roof  should  be  assumed  to  be  at  a  temperature  of  32°. 
Then,  in  addition  to  the  loss  figured  in  Example  1, 
there  will  have  to  be  added  the  loss  due  to  the  tin 
roof.  The  area  of  the  ceiling  of  the  room  would  be 
14x20=280  square  feet.  Referring  to  Table  IV  we 
find  the  loss  per  hour  through  ceilings  of  plaster  con- 
struction to  be  .62  B.  t.  u.  per  degree  difference  of 
temperature;  then  the  loss  through  this  ceiling  would 
be,  per  degree  of  temperature,  .62X280=173.6  B.  t 
u.  The  room  being  at  70°  and  the  attic  space  32°, 
the  difference  in  temperature  would  be  70 — 32=38 
degrees.  The  total  loss  through  the  ceiling  would 
then  be  29.1X38=6,574  B.  t.  u.  Adding  this  to  the 
loss  found  in  Example  1  we  have  a  total  loss  from  the 
room,  5,075+6,574=11,649  B.  t.  u. 

A  more  accurate  method  is  to  figure  the  actual  loss 
through  the  walls  and  windows  from  the  constants 
in  tables  IX  and  X. 

The  loss  from  walls  (.24X170)  70= 2,856 

The  loss  from  windows  (1.03X30)  70= 2,163 


Total  loss  from  walls  and  windows= 5,019 

To  allow  for  diffusion  this  sum  must  be  multiplied 
by  iy2,  making  a  gross  loss  of  7,528. 


27 


CHAPTER  II. 

DIFFERENT  FORMS  OF  HEATING. 

Classification  of  Heating  Apparatus. — The  different 
heating  systems  may  be  classed  under  two  general 
heads — Direct  and  Indirect.  In  direct  heating  the 
heating  surfaces  are  placed  in  the  rooms  to  be  heated, 
as,  for  instance,  stoves,  steam  radiators  or  hot  water 
radiators.  In  indirect  heating  systems  the  heating 
apparatus  is  placed  in  some  other  room  and  the  heat 
carried  to  the  -room  to  be  heated  by  means  of  pipes. 
Under  this  head  would  be  included  hot  air  furnaces 
and  the  various  systems  of  heating  in  which  fresh 
cold  air  is  made  to  pass  over  steam  or  hot  water  radi- 
ators on  its  way  to  the  room. 

The  indirect  systems  of  heating  naturally  divide 
themselves  into  two  other  classes,  those  using  natural 
draft  and  those  using  forced  draft.  A  good  example 
of  natural  draft  indirect  heating  is  the  hot  air  furnace, 
where  the  circulation  of  air  through  the  house  is  pro- 
duced by  the  difference  in  temperature  between  the 
air  in  the  hot  air  flues  and  the  cold  air  outside  the 
flues.  The  fan  system  of  heating,  used  in  heating 
school  buildings  and  churches,  are  good  examples  of 
the  forced  draft  system.  In  this  case  the  draft  is 
largely  produced  by  mechanical  means,  usually  a 
disc  fan  or  a  pressure  blower. 

In  order  to  understand  better  a  discussion  of  the 
various  forms  of  heating  which  will  come  later,  it  is 
desirable  to  understand  in  general  the  advantages  and 
disadvantages  of  the  various  forms  of  heating. 

Grates, — The  most  primitive  form  of  heating  ap- 

38 


Notes          on          Heating          and          Ventilation 

paratus  is  the  grate.  In  the  grate  the  air  which  passes 
through  the  fire  and  is  heated  by  the  fire  all  passes  up  the 
chimney  and  only  the  heat  given  off  by  radiation  to  the 
walls  and  objects  in  the  room  is  effective  in  heating  the 
room.  In  grates  of  better  construction  this  is  somewhat 
improved  by  surrounding  the  grate  by  fire  brick  so 
arranged  that  the  brick  will  become  highly  heated  and 
radiate  heat  to  the  room.  But  the  fact  that  all  the 
air  heated  by  the  grate  passes  up  the  stack  makes 
this  a  very  uneconomical  form  of  heating.  In  the 
best  form  of  open  grates  only  about  20  per  cent  of 
the  heat  of  the  fuel  is  effective  in  heating  the  room. 
This  form  of  heating,  however,  has  been  defended  by 
many.  It  is  a  very  popular  form  of  heating  through- 
out England  and  Scotland.  The  feeling  of  a  grate- 
heated  room  is  quite  different  from  that  of  a  room 
heated  by  other  systems.  All  the  heat  is  given  off 
by  radiation  and  the  air  in  a  grate-heated  room  is  at 
a  considerably  lower  temperature  than  the  objects  and 
persons  in  the  room,  owing  to  the  fact  that  radiated 
heat  does  not  heat  the  air  through  which  it  passes. 
The  air  of  the  room  being  at  a  lower  temperature, 
its  capacity  for  moisture  is  not  increased  as  much 
as  it  would  be  were  the  air  heated  to  a  higher  tem- 
perature. The  result  is  that  the  air  contains  propor- 
tionally more  moisture  than  is  the  case  in  other  forms 
of  heating.  This,  no  doubt,  is  an  advantage.  On  the 
other  hand,  it  is  impossible  to  he'at  the  room  uni- 
formly, and  a  person  is  hot  or  cold,  depending  upon 
his  distance  from  the  grate.  Heating  by  means  of 
grates  is  practiced  only  in  the  more  moderate  climates. 
The  grate  is  useful  in  the  houses  heated  by  other 
forms  of  heating,  as  it  serves  as  a  most  efficient  foul 

29 


Notes          on          Heating          and          Ventilation 

air  flue.  The  introduction  of  a  large  number  of  grates 
into  a  house  adds  materially  to  the  ease  with  which 
the  house  may  be  ventilated. 

Stoves. — The  stove  is  a  marked  improvement  over 
the  grate  as  a  form  of  heating,  particularly  from  the 
standpoint  of  economy.  The  modern  base  burner 
stove  is  one  of  the  most  economic  and  efficient  forms 
of  heating,  making  use  of  from  70  to  80  per  cent  of 
the  heat  in  the  fuel.  In  heating  by  a  stove  the  heat 
is  .given  off  both  by  radiation  and  by  convection.  The 
hot  surface  of  the  stove  being  at  a  higher  tempera- 
ture than  the  surrounding  objects  in  the  room,  radiates 
its  heat  directly  to  these  objects.  In  addition  the 
air  surrounding  the  stove  is  heated  and  rises,  passing 
along  the  ceiling  to  the  cold  wall  and  window  sur- 
faces where  it  is  cooled,  drops  to  the  floor  and  passes 
along  the  floor  back  to  the  stove  to  be  again  heated. 
In  selecting  a  stove  to  heat  a  given  room  care  should 
be  taken  to  select  one  of  ample  size  so  that  only  in 
the  coldest  weather  would  it  be  necessary  to  crowd 
it;  that  is,  keep  on  the  drafts  in  order  to  heat  the 
room.  At  the  present  time  the  stove  as  a  general 
source  of  heat  is  being  rapidly  discarded  because  of 
the  attendance  required,  the  space  occupied  and  the 
unsightly  appearance  of  the  stove.  Another  serious  ob- 
jection to  the  stove  is  the  fact  that  it  does  not  furnish 
ventilation  to  the  room  which  it  heats. 

Hot  Air  Furnaces. — The  hot  air  furnace  is  a  natural 
outgrowth  of  the  stove.  In  this  system  one  large 
stove  is  placed  in  the  basement  of  the  building,  the 
air  is  taken  from  the  outside,  passed  over  the  sur- 
faces of  the  stove  or  furnace,  carried  up  through  the 
flues  to  the  rooms  to  be  heated.  The  principal  ad- 

30 


Notes          on          Heating          and          Ventilation 

vantage  of  the  hot  air  furnace  is  that  it  provides  a 
cheap  method  of  furnishing  both  heat  and  ventilation, 
it  requires  little  attendance  and  does  not  deteriorate 
rapidly  when  properly  taken  care  of.  The  greatest 
disadvantage  of  this  system  is  in  the  fact  that  the 
circulation  of  the  heated  air  depends  entirely  upon 
natural  draft ;  that  is,  it  depends  upon  the  difference 
in  weight  between  the  air  inside  the  flue  and  the  air 
outside  the  flues.  This  difference  of  weight  is  ex- 
tremely small,  so  that  the  force  producing  circulation 
in  the  flue  is  always  small.  This  force  is  easily  over- 
come either  by  the  winds  or  by  the  resistance  of  the 
piping.  When  a  very  strong  wind  blows  against  one 
side  of  the  house  it  is  difficult  to  heat  the  rooms  on 
that  side  of  the  house.  If  the  system  is  carefully  de- 
signed, however,  this  difficulty  can  be  overcome  in 
a  measure.  Another  serious  objection  to  the  hot  air 
furnace  is  that  it  is  seldom  dust  tight  and  dust  and 
ashes  are  carried  into  the  room.  In  general,  how- 
ever, the  hot  air  furnace  may  be  considered  as  a 
very  good  type  of  heating  plant  for  small  residences. 
In  the  case  of  the  hot  air  furnace  the  heat  is  carried 
to  the  room  by  convection,  as  all  heat  is  carried  from 
the  furnace  by  the  air  which  passes  around  the  fur- 
nace and  enters  the  rooms  from  the  flues.  This  air 
circulates  in  the  room  and  heats  the  objects  and  air 
in  the,  room.  The  efficiency  of  the  hot  air  system 
will  vary,  depending  on  the  relative  proportion  of  the 
air  taken  from  outside  and  upon  the  temperature  of 
the  air  entering  the.  room.  If  the  cold  air  entering 
the  furnace  is  taken  from  the  house  itself  and  not  from 
outside,  the  efficiency  of  the  hot  air  furnace  will  be 
almost  the  same  as  that  of  a  steam  furnace;  that  is, 

31 


Notes         on          Heating         and         Ventilation 

from  70  to  75  per  cent  of  the  heat  of  the  coal  will 
go  into  the  rooms.  If,  however,  the  cold  air  is  taken 
from  outside,  then  the  heat  used  in  heating  the  air 
from  the  temperature  of  the  outside  air  to  the  tem- 
perature of  the  room  will  be  lost,  and  under  ordinary 
conditions  of  operation  the  efficiency  would  be  from 
50  to  60  per  cent. 

Steam  Heating  Direct. — From  the  standpoint  of 
ventilation  direct  steam  heat  has  little  advantage  over 
a  stove,  as  it  gives  no  means  of  supplying  fresh  air. 
Its  use  in  general  should  be  confined  to  rooms  which 
require  little  or  no  ventilation.  Mechanically,  how- 
ever, it  has  many  advantages  over  the  stove  or  the 
hot  air  furnace.  The  boiler  for  a  building  having 
this  form  of  heating  can  be  located  anywhere  in  the 
basement,  and  the  rooms  are  free  from  dirt  or  gas. 
The  modern  radiator  is  easily  adapted  to  almost  any 
location  in  the  room,  it  is  not  affected  by  wind  or 
local  conditions,  and  a  distant  room  may  be  heated 
as  easily  as  one  close  to  the  furnace.  The  efficiency 
of  the  direct  steam  heating  system  is  less  than  that 
of  a  stove,  with  a  well-installed  plant  from  60  to  70 
per  cent  of  the  heat  of  the  fuel  will  be  delivered  by 
the  radiator  to  the  room. 

Hot  Water,  Direct. — The  application  of  direct  hot 
water  radiators  as  a  method  of  heating  is  similar  to 
that  of  steam,  with  the  exception  that  the  surfaces 
are  at  a  much  lower  temperature  and  hence  more 
radiating  surface  will  be  required.  It  has  an  advan- 
tage over  steam  in  that  the  temperature  of  the  heat- 
ing surface  can  be  controlled  easily,  and  can  be  any- 
where from  the  temperature  of  the  room  to  180 
degrees.  It  also  has  the  advantage  that  the  surface 

32 


Notes         on         Heating         and         Ventilation 

of  the  radiator  being  at  a  lower  temperature  gives  off 
more  heat  by  convection  and  less  by  radiation.  This 
gives  the  room  more  nearly  the  condition  of  Summer 
and  the  heating  is  not  apparent  to  the  occupants  of 
the  room.  In  the  steam  radiator  the  surface  is  usu- 
ally not  less  than  212  degrees.  The  principal  disad- 
vantage of  this  system  is  in  the  fact  that  the  circula- 
tion of  the  system  is  by  natural  circulation;  that  is, 
the  circulation  is  produced  by  a  difference  in  weight 
between  the  water  in  the  hot  leg  of  the  system  and 
in  the  cold  leg  of  the  system.  This  difference  in  tem- 
perature is  usually  about  10  degrees,  so  that  the 
difference  in  weight  between  these  two  columns  of 
water  is  small  and  the  resulting  force  producing  circu- 
lation is,  of  course,  small.  It  is  necessary  to  be  very 
careful  in  designing  the  piping  for  the  hot  water  sys- 
tem, as  the  circulation  may  be  easily  affected  by  the 
height  of  the  radiator  above  the  boiler;  the  greater 
the  height  above  the  boiler,  the  greater  will  be  the 
difference  in  weight  between  the  two  columns  of  water 
and  the  stronger  will  be  the  force  producing  circula- 
tion. This  system  in  general  requires  more  careful 
design  and  construction  than  the  steam  system.  The 
efficiency  of  the  hot  water  system  is  practically  the 
same  as  that  of  steam,  and  we  may  expect  to  obtain 
in  the  room  from  60  to  70  per  cent  of  the  heat  in 
the  coal. 

Indirect  Steam  Heating. — In  heating  with  indirect 
steam  radiation  cold  air  is  drawn  from  the  outside, 
passed  through  and  around  the  hot  radiator,  which  is 
usually  situated  in  the  basement,  and  delivered  by 
pipes  to  the  rooms  to  be  heated.  The  rules  governing 
the  introduction  of  air  into  the  rooms  and  the  method 

33 


Notes         on         Heating         and         Ventilation 

of  running  pipes  is  similar  to  that  employed  with  hot 
air  furnaces.  The  principal  advantages  of  indirect 
steam  over  hot  air  are:  Each  room  has  a  separate 
source  of  heat,  the  system  is  not  affected  by  the  winds 
and  no  dust  or  obnoxious  gases  are  carried  to  the 
rooms. 

The  air  entering  the  room  will  always  be  as  pure 
as  the  air  which  furnishes  the  source  of  supply.  The 
source  of  heat  being  independent  of  the  position  of  the 
boiler,  it  is  possible  to  place  the  indirect  radiator  any- 
where in  the  building  and  long  hot  air  pipes  are  not 
necessary.  This  makes  the  indirect  radiator  much 
more  efficient  and  more  certain  in  operation  than  the 
hot  air  furnace.  The  efficiency  of  this  system,  from 
the  standpoint  of  coal  consumption,  will  be  much  less 
than  in  direct  forms  of  heating  and  about  the  same  as 
the  hot  air  furnace;  that  is,  from  50  to  60  per  cent  of 
the  heat  of  the  coal  will  be  used  effectively  in  heating. 

Indirect  Hot  Water  Heating. — The  application  of 
hot  water  indirect  is  similar  to  that  of  steam  and  the 
efficiency  is  practically  the  same.  The  use  of  hot 
water  indirects  has  been  much  more  limited  than  the 
use  of  steam  indirects.  The  installation  of  hot  water 
indirects  must  be  done  with  great  care  so  that  each 
radiator  will  at  all  times  have  the  proper  amount  of 
hot  water  circulation  through  it.  In  the  hot  water 
indirect  radiators,  if  for  any  reason  the  water  in  the 
radiator  becomes  cooled,  the  radiator  will  be  in  danger 
of  freezing.  In  mild  climates  this  difficulty  would 
not  be  as  serious  as  in  locations  where  the  weather  is 
extremely  cold. 

Fan  System  of  Heating. — In  buildings  of  a  public 
or  semi-public  character,  where  a  large  number  of 

34 


Notes         on         Heating         and         Ventilation 

people  are  to  be  assembled  in  a  relatively  small  space, 
it  is  necessary  to  provide  adequate  ventilation.  In  the 
systems  that  have  been  previously  described  it  is  im- 
possible to  introduce  into  the  room  sufficient  quanti- 
ties of  air  to  ventilate  the  rooms  properly.  It  may 
be  said  in  general  that  no  system  of  natural  circulation 
has  ever  produced  satisfactory  ventilation  in  a  room 
occupied  by  a  large  number  of  people;  it  is  necessary 
to  provide  some  means  of  mechanically  circulating  the 
air.  This  is  done  in  the  fan  system  by  means  of  a 
pressure  blower  or  a  disc  fan. 

In  the  fan  system  the  pressure  produced  by  the  fan 
makes  the  circulation  so  positive  that  it  is  not  affected 
by  winds  or  by  the  distance  of  the  room  from  the  fan 
itself.  The  air  is  taken  from  the  outside,  passed 
through  the  heating  coils  and  forced  into  the  building 
by  the  fan. 

There  are  two  general  methods  of  heating  and  ven- 
tilating with  the  fan  system.  In  one  system  the  air 
is  first  passed  through  a  tempering  coil,  then  taken 
by  the  fan  and  delivered  through  a  heating  coil.  Each 
room  has  a  connection  both  to  the  hot  air  and  to 
the  tempered  air  chamber.  The  temperature  of  the 
air  in  the  room  is  adjusted  by  taking  the  air  either 
from  the  hot  air  chamber  or  from  the  tempered  air 
chamber.  In  the  second  system  the  rooms  them- 
selves are  heated  by  means  of  direct  radiation  and 
the  fan  delivers  air  to  the  rooms  only  for  the  purpose 
of  ventilation.  In  this  case  no  heating  coils  would 
be  necessary. 

In  the  first  method  the  economy  of  the  system  is 
low,  as  owing  to  the  large  amount  of  air  required 
for  ventilation  and  the  quantity  of  air  introduced  into 

35 


Notes         on         Heating         and         Ventilation 

the  room  is  ordinarily  greater  than  is  necessary  for 
the  purpose  of  heating  the  room.  The  economy  of  this 
form  of  fan  system  depends  very  largely  upon  the 
amount  of  air  necessary,  but  in  most  cases  its  effi- 
ciency would  not  exceed  from  40  to  50  per  cent;  that 
is,  only  40  to  50  per  cent  of  the  heat  units  in  the 
coal  would  be  effective  in  heating.  In  the  combined 
fan  system,  where  direct  radiation  is  used  for  heat- 
ing and  the  fan  system  for  ventilation,  the  economy 
of  the  system  is  better,  probably  from  50  to  60  per 
cent. 

The  increase  in  economy  of  this  system  is  due  to 
the  fact  that  it  is  necessary  to  run  the  fans  only  when 
it  is  necessary  to  ventilate  the  building. 

Combination  of  Different  Systems. — In  addition  to 
the  combination  just  described,  of  direct  radiation  and 
fan  ventilation,  there  have  been  devised  innumerable 
combinations,  combinations  of  direct  and  indirect 
steam,  direct  and  indirect  water,  water  and  hot  air, 
steam  and  hot  air.  Probably  the  combinations  which 
have  been  most  used  have  been  combinations  of  direct 
and  indirect  steam  and  the  combinations  of  hot  water 
and  hot  air. 

The  Economy  of  Different  Systems. — The  economy 
of  any  heating  system  depends  upon  the  completeness 
with  which  the  coal  in  the  furnace  is  burned  and  the 
heat  lost  by  the  chimney  and  the  ventilating  flues. 
If,  with  each  of  the  above  systems  the  coal  was  com- 
pletely burned  and  all  the  heat  given  off  were  used, 
then  each  one  of  the  systems  would  have  perfect 
efficiency. 

The  losses  from  any  system,  given  in  detail,  are  as 
follows :     Loss  through  imperfect  combustion  of  coal,  • 
through  the  escape  of  hot  gases  up  the  chimney  and  the 

36 


Notes          on          Heating          and          Ventilation 

loss  of  heat  in  the  air  passing  up  the  ventilating  flue. 

If  the  furnace  is  properly  constructed  and  insures 
good  combustion,  the  loss  due  to  imperfect  combustion 
is  small.  The  loss  of  heat  passing  up  the  chimney  will 
depend  upon  the  temperature  at  which  the  gases  leave 
the  chimney  and  the  amount  of  air  used  to  burn  a  pound 
of  coal.  The  loss  bv  the  ventilating  flue  will  depend 
upon  the  amount  of  air  it  is  necessary  to  supply  to 
the  rooms  for  ventilation. 

If  the  hot  gases  leave  the  heating  apparatus  at  the 
same  temperature  and  the  same  amount  of  air  is  used  for 
ventilation,  then  the  efficiency  of  each  system  will  be 
practically  the  same.  If  the  rooms  are  not  ventilated, 
then,  of  course,  the  loss  due  to  the  heat  passing  up  the 
ventilating  flues  will  be  saved  and  the  system  will  be 
more  economical.  In  fact,  strictly  speaking,  the  loss  by 
ventilation  should  not  be  considered  as  entering  into  the 
efficiency  of  the  svstem.  This  loss  is  entirely  independent 
of  the  system  used  and  depends  entirely  upon  the  amount 
of  air  which  must  be  supplied  for  purpose  of  ventilation. 
It  is  quite  obvious  that  any  system  involving  ventilation 
will  require  a  greater  amount  of  coal.  The  loss  due  to 
ventilation  is  due  to  the  fact  that  all  the  heat  which  is 
given  to  the  air  between  the  temperature  of  the  air  out- 
side the  building  and  the  air  in  the  room  is  ineffective  in 
heating  and  is  lost  up  the  ventilating  flues.  It  would 
be  poor  policy,  however,  for  the  designers  of  heating 
systems  to  cut  down  the  amount  of  ventilation  in  a  room 
in  order  to  save  coal.  In  several  states  there  are 
p-eneral  state  laws  which  require  that  a  certain  amount 
of  air  be  furnished  each  person  per  hour  in  school 
buildings  and  other  buildings  of  a  public  character. 
The  necessity  and  importance  of  ventilation  will  be 
discussed  under  another  head. 

37 


CHAPTER  III. 

THE  DESIGN  OF  A  DIRECT  STEAM-HEATING 
SYSTEM. 

Steam  heating  is  usually  done  by  direct  or  by  indirect 
radiation  or  by  combination  of  both  direct  and  indirect 
radiation.  In  small  residences  occupied  by  only  three  or 
four  persons  it  is  customary  to  use  only  direct  radiation. 
The  practice,  however,  is  a  questionable  one,  and  it  seems 
desirable,  even  in  small  residences,  that  some  indirect 
radiation  be  used  so  as  to  provide  a  means  of  ventila- 
tion. Oftentimes  only  one  indirect  radiator  is  used, 
bringing  its  air  either  into  the  room  most  used  or  into 
the  main  hall  so  that  it  may  be  distributed  throughout 
the  house.  In  factories  and  office  buildings  where  a* 
large  amount  of  air  is  introduced  by  the  opening  and 
closing  of  doors  it  is  customary  to  use  only  direct  radia- 
tion, and  in  such  buildings  this  is  permissible. 

Nature  and  Properties  of  Steam. — In  order  to  under- 
stand thoroughly  the  operation  of  a  steam  heating  system 
the  nature  and  properties  of  steam  should  be  studied. 
Steam  is  a  watery  vapor,  and  as  used  in  ordinary  radiator 
practice  always  contains  a  certain  amount  of  water  in 
suspension,  as  does  the  atmosphere  in  foggy  weather. 

When  water  is  heated  in  a  steam  boiler  the  tempera- 
ture is  slowly  increased  from  the  initial  temperature  of 
the  water  to  the  temperature  of  the  boiling  point.  When 
the  water  reaches  the  boiling  point  small  particles  of  the 
water  are  changed  from  water  to  steam,  rise  through  the 
mass  of  water  and  escape  to  the  surface;  the  water  is 
then  said  to  boil.  The  temperature  at  which  the  water 
boils  depends  entirely  upon  the  pressure  in  the  boiler  and 


Notes         on          Heating         and         Ventilation 

obviously,  as  the  boiling  point  increases  more  and  more, 
heat  is  required  to  produce  steam. 

Take,  for  instance,  a  given  case.  Suppose  we  start 
with  water  in  the  boiler  at  40  degrees  and  the  pressure 
in  the  boiler  at  atmospheric  pressure,flhat  is,  14.7  pounds. 
Under  this  condition  it  will  be  necessary  to  increase  the 
temperature  of  the  water  in  the  boiler  to  212  degrees,  at 
which  point  water  will  commence  to  boil.  It  will  be  nec- 
essary to  add  212 — 40=172  B.  t.  u.  for  every  pound 
of  water  in  the  boiler.  In  order  to  convert  all  the  water 
into  steam  it  will  be  necessary  to  supply  965.7  heat  units 
for  each  pound,  in  addition  to  the  172  heat  units  con- 
sumed in  raising  the  water  to  the  boiling  point.  During 
the  operation  of  boiling,  however,  the  temperature  of 
the  water  remains  constant  and  the  966  heat  units  added 
in  order  to  change  the  water  at  the  temperature  of  the 
boiling  point  into  steam  are  consumed  in  separating  the 
molecules  of  water  and  changing  the  water  from  a  liquid 
into  a  gas.  This  last  quantity  is  termed  the  latent  heat 
and  it  is  the  latent  heat  of  water  which  is  used  primarily 
in  furnishing  heat  to  the  room  in  steam  heating.  As  the 
pressure  in  the  boiler  increases  the  latent  heat  diminishes. 
The  relation  of  these  various  quantities  has  been  very 
carefully  determined  by  Regnault  and  compiled  in  the 
form  of  steam  tables.  The  following  is  an  abbreviated 
steam  table.  More  complete  tables  will  be  found  in  Pea- 
body's  Steam  Tables,  or  in  any  of  the  mechanical  engi- 
neering handbooks. 

STEAM  TABLES. 

Column  1  of  the  Steam  Table  gives  the  pressure  of  the 
steam  above  the  atmosphere  in  pounds  per  square  inch 
and  below  the  atmosphere  in  inches  of  mercury.  Column 
2  gives  the  corresponding  temperature  of  the  steam. 

39 


Notes         on         Heating         and         Ventilation 

Column  3  gives  the  heat  of  the  liquid  or  the  heat  neces- 
sary to  raise  one  pound  of  water  from  32  degrees  to  the 
temperature  of  the  boiling  point,  corresponding  to  the 
pressure.  Column  4  gives  the  latent  heat  necessary  to 
change  a  pound  of  %ater  at  the  temperature  of  the  boil- 
ing point  into  steam  at  the  same  temperature.  Column 
5  is  the  sum  of  columns  3  and  4,  and  represents  the 
amount  of  heat  necessary  to  raise  a  pound  of  water  from 
32°  to  the  boiling  point  and  then  change  it  into  steam 
at  the  temperature  of  the  boiling  point.  The  quantities 
given  in  this  column  are  called  total  heat.  Column  6 
gives  the  volume  of  one  pound  of  steam  at  the  differ- 
ent pressures. 


Pressure 

TABLE  XIV—  PROPERTIES  OF  STEAM. 

or  Vacuum. 

Volume  of 

Inches 

Tempera- 

Heat of 

Latent 

Total 

1  Ib.  of 

Mercury 

ture 

the  Liquid 

Heat 

Heat 

Steam 

—24 

137 

105 

1,019 

1,124 

135 

—20 

160 

128 

1,003 

1,131 

78.3 

—16 

175 

143  ' 

992 

1,135    ' 

55.9 

—14 

187 

155 

984 

1,139 

43.6 

—  8 

197 

165 

977 

1,142 

35.8 

—  2 

205 

173 

971 

1,144 

30.6 

Pounds 

per  sq.  in. 

0 

212 

180.9 

965.7 

1,146.6 

26.38 

1 

215 

184 

964 

1.148 

25 

2 

219 

188 

961 

1,149 

23 

3 

222 

191 

959 

1,150 

22.3 

4 

224 

193 

957 

1.150.5 

21.2 

5 

227 

196 

955 

1,151 

20.16 

10 

239 

208 

946  - 

1,154 

16.3 

15 

249 

218.8 

939.3 

1,158.1 

13.7 

20 

258.7 

228 

932.5 

1,161 

11.85 

25 

266.7 

236.2 

927.1 

1,163.3 

10.36 

30 

273.9 

243.5 

922 

1,165.5 

9.34 

35 

280.5 

250.2 

917.3 

1,167.5 

8.45 

40 

286.5 

256.3 

913 

1,169.3 

7.73 

45 

292.2 

262.1 

909 

1,171.1 

7.11 

50 

297.5 

267.5 

905.2 

1,172.7 

6.61 

55 

302.4 

272.6 

901.6 

1,174.2 

6.16 

60 

307.1 

277.2 

898.4 

1,175.6 

5.77 

65 

311.5 

281.8 

895.1 

1,176.9 

5.43 

70 

315.8 

286.1 

892.1 

1,178.2 

5.13 

75 

319.8 

290.3 

889.1 

1,179.4 

4.86 

80 

323.7 

294.3 

886.3 

1,180.6 

4.63 

85 

327.4 

298.1 

883.6 

1,181.7 

4.41 

90 

330.9 

301.8 

881 

1,182.8 

4.20 

95 

334.4 

305.4 

878.5 

1,183.9 

4.02 

100 

337.6 

308.9 

876 

1,184.9 

3.83 

110 

•      343.9 

315.4 

871.4 

1,186.8 

3.57 

120 

349.8 

321.5 

867.1 

1,188.6 

3.33 

130 

355 

327.5 

863 

1,190.3 

3.1 

140 

360 

333.5 

859.1 

1,191.9 

2.92 

150 

365.7 

338.3 

855.4 

1,193.4 

2.75 

40 


Notes         on          Heating         and         Ventilation 

EXAMPLES  IN  USE  OF  STEAM  TABLE. 

EXAMPLE  1. — It  is  required  to  convert  10  pounds  of 
water  at  32°  into  steam  at  100  pounds  gauge  pressure. 

SOLUTION. — We  see  from  column  5  that  the  total  heat 
of  1  pound  of  steam  at  100  pounds  pressure  is  1,184.9 
heat  units.  Then  to  form  10  pounds  of  steam  would 
require  10  times  this  amount,  of  11,849  heat  units. 

2.  How  many  heat  units  will  be  required  to  form  5 
pounds  of  steam  from  feed  water  at  100°  in  tempera- 
ture into  steam  at  10  pounds  gauge  pressure? 

SOLUTION. — The  total  heat  of  steam  at  10  pounds  pres- 
sure above  32°  is  1,154  heat  units.  In  this  case  the  feed 
water  already  contains  in  it  above  32°,  100  —  32  =  68 
heat  units.  The  specific  heat  of  water  being  1,  the  heat 
units  required  to  forfn  a  pound  of  steam  will  be  1,154 
—  68  =  1,086,  and  to  form  5  pounds  of  steam  would  re- 
quire 5  X  1,086  =  5,430. 

3.  A  steam  pipe  is  8  inches  in  diameter.    The  pressure 
of  steam  in  the  pipe  is  10  pounds  gauge.     The  steam 
pipe   is  to  transmit   1,600  pounds  of  steam  per  hour. 
What  will  be  the  velocity  of  steam  in  the  pipe? 

SOLUTION.— From  column  6  of  the  table  we  see  that 
the  volumn  of  1  pound  of  steam  at  10  pounds  gauge  pres- 
sure is  16.3  cubic  feet.  Then  1,600X16.3=26,080  cubic 
feet,  the  volume  of  steam  passing  per  hour.  This  divided 
by  3,600  equals  72,  the  number  of  cubic  feet  passing  per 
second.  An  8-inch  pipe  has  an  area  of  50  square  inches ; 
50-^144=.347  square  feet;  72-^.347=208  feet  per  sec- 
ond, which  represents  the  velocity  of  the  steam  passing 
through  the  pipe.  This  velocity  is  very  high.  Ordinarily 
the  velocity  in  steam  pipes  should  not  exceed  100  feet 
per  second,  even  in  very  large  pipes. 

41 


Notes         on         Heating         and         Ventilation 

LOSS  OF  HEAT  FROM  RADIATORS. 

In  designing  a  direct  steam  system  it  will  be  necessary 
first  to  compute  the  heat  losses  from  the  various  rooms 
by  the  rules  previously  given.  After  these  losses  are 
determined  it  will  be  necessary  to  place  sufficient  radi- 
ating surface  in  the  room  to  supply  these  losses.  In 
order  to  know  the  amount  of  surface  that  should  be 
placed  in  a  room  it  is  necessary  to  know  the  amount  of 
heat  given  off  per  square  foot  by  the  different  forms  of 
radiators.  Heat  losses  for  the  different  forms  of  direct 
radiators  are  given  in  the  following  table: 

TABLE    XV— LOSS    FROM    WROUGHT    IRON    PIPE    AND    CAST 
IRON   RADIATORS. 


I     si 

gig 

^  OB  C 

g.§         OS*       -ufcfl 
r*  Js  o        £  o  +:       „•  «>  S  £  o 

fcH4-p^        KvZi       FQftro-i->t, 

C&st  Iron  Radiators,   38  Inches. 

1  column.    .  .  .48      sq.   ft. 

226 

105 

.212 

1.82 

2  column. 

...48      sq.    ft. 

226 

76 

.253 

1.65 

3  column. 

...45.3  sq.  ft. 

226 

88 

.204 

1.42 

6  column. 

...36       sq.   ft. 

225 

71 

.217 

1.35 

Wrought   Iron 

Radiators, 

38   Inches. 

1  column. 

...12      sq.   ft. 

221 

89 

.446 

3.27 

2  column. 

..42      sq.   ft. 

222 

83 

.284 

2. 

3  column  48      sq.  ft. 

229 

70 

.294 

1.77 

4  column  48      sq.   ft. 

226 

73 

.202 

1.27 

1"  wall  coi 
1"  wall  coi 

1    1  pipe  high 

212 

228 

70 
65 

.41 
.425 

2.8 

2.48 

1     4    nines   hie-h 

Colonial  wall  coil.. 

212 

70 

.330 

2.25 

Column  5  is  the  column  which  shows  the  relative  effec- 
tiveness of  the  various  types  of  radiators.  It  is  obtained 
in  the  following  manner:  Take,  for  example,  the  two- 
column  cast  iron  radiators,  results  of  which  are  given  in 
line  2  of  the  table.  A  pound  of  steam  at  226°,  as  we  see 
from  the  steam  tables,  gives  up  its  latent  heat  in  con- 
densing which  amounts  to  965  heat  units.  This  radiator 

42 


Notes 


on 


Heating          and          Ventilation 


condensed  .253  pounds  of  steam  per  square  foot  of  sur- 
face per  hour.  Then  965 X -253=247,  the  heat  units 
given  up  by  the  radiator  per  square  foot  per  actual  sur- 
face per  hour.  The  steam  in  the  radiator  was  at  a  tern- 


Fig.  9.      Single-Column   Cast   Iron   Radiator. 

perature  of  226°  and  the  air  in  the  room  at  a  tempera- 
ture of  76°,  the  difference  in  temperature  being  150°.  If 
we  divide  M7  by  150  the  result  is  approximately  1.65. 
This  result  represents  the  B.  t.  u.  transmitted  per 

43 


Notes 


o  n 


Heating         and         Ventilation 


square  foot  of  rated  surface  per  hour  per  degree  differ- 
ence of  temperature  between  the  steam  inside  the  radi- 
ator and  the  air  in  the  room.  This  is  the  quantity  which 
should  be  used  in  comparing  the  relative  merits  of  the 
various  forms  of  heating  surfaces. 

The  results  of  a  series  of  experiments  made  at  the 


o  o 


Fig.  10. 

University  of  Michigan,  extending  over  a  period  of 
a  number  of  years,  together  with  the  results  shown 
in  the  foregoing  table,  lead  to  the  following  conclusions : 
Different  Types  of  Relative  Efficiency. — Radiators 
with  different  steam  volumes  do  not  give  essentially 

44 


Notes         on          Heating         and         Ventilation 

different  results,  except  as  the  volume  is  so  small  as 
to  restrict  the  passage  of  steam.  Single  column  radi- 
ators, as  shown  in  Fig.  9,  usually  show  larger  results 
than  those  with  more  than  one  column.  The  con- 
densation per  square  foot  of  radiator  per  degree  differ- 
ence of  temperature  as  shown  in  column  5  of  Table  VII 
shows  a  rapid  decrease  as  the  number  of  columns  in- 
creases. The  reason  for  this  is  quite  apparent  when  we 
consider  the  position  of  the  radiating  surfaces  in  a 
single  pipe  radiator  as  compared  with  the  surface  in  a 
three-pipe  radiator.  Referring  to  Fig.  10,  tube  B,  you 
will  note  that  this  tube  can  radiate  heat  in  all  directions 
without  interference,  except  those  lines  which  radiate 
to  columns  A  and  C.  Columns  A  and  C  being  at  the 
same  temperature,  no  radiant  heat  passes  between  them, 
so  that  all  the  surface  of  column  B  which  would  radiate 
its  heat  to  columns  A  and  C  is  unaffected.  The  amount 
of  surface  which  does  this,  however,  is  extremely  small. 

Suppose  we  take  point  1  on  column  B.  The  heat 
from  that  point  radiates  in  a  straight  line  in  all  direc- 
tions. But  all  the  rays  of  heat  between  ray  2  and  ray  3 
strike  on  column  A  and  are  lost  because  column  A  is 
the  same  temperature  as  column  B.  The  number  of  rays 
that  do  this  are  extremely  small  in  a  single  column 
radiator. 

If  we  consider  column  B  in  a  three-column  radiator 
and  take  point  1  on  column  B  we  see  that  all  the  rays 
between  2  and  3,  4  and  5,  6  and  7,  8  and  9,  10  and  11 
are  lost  and  become  ineffective  for  heating  as  columns 
A,  C,  D,  E,  F,  are  at  the  same  temperature  and  intercept 
rays  passing  into  the  room. 

45 


Notes 


o  n 


Heating         and 


Ventilation 


When  the  columns  in  a  radiator  have  been  increased 
from  5  to  6  then  the  inner  columns  have  practically  no 
effect  in  giving  off  radiant  heat,  and  the  only  heat  they 


Fig.    11.      Two-Column    Cast    Iron    Radiator. 

give  off  is  given  by  convection  due  to  the  passage  of 
air  through  the  radiator. 

By  glancing  at  Fig.  10  we  see  that  the  greater  the 
distance  between  the  columns  or  pipes  of  a  radiator  the 
smaller  would  be  the  number  of  rays  of  radiant  heat 

4G 


Notes         on         Heating         and         Ventilation 

intercepted  by  other  columns  of  the  radiator  and  the 
larger  would  be  the  radiating  effect;  the  wider  the 
space  between  the  columns  of  the  radiator  the  more 
effective  does  the  radiator  become  in  giving  off  heat. 

The  writer  has  had  opportunity  to  make  a  series  of 
tests  on  radiators  of  the  two-column  type,  having  the 
sections  of  one  radiator  spaced  at  %l/2  inches  and  the  sec- 
tions of  the  other  radiator  3*/£  inches.  The  increase  of 
y%  inch  in  the  length  of  space  added  approximately  10 
per  cent  to  the  effectiveness  of  the  radiator. 

Radiators  are  made  in  standard  heights.  The  height 
most  used  is  38  inches.  They  can  be  purchased,  however, 
in  varying  heights  from  15  to  45  inches.  The  radiators 
of  various  heights  are  rated  at  a  certain  number  of 
square  feet  per  section.  For  instance,  a  38-inch  two- 
column  radiator,  as  shown  in  Fig.  11,  is  rated  at  4  square 
feet  per  section.  As  a  rule,  however,  radiators  are 
slightly  overrated.  A  radiator  containing  48  square  feet 
has  an  actual  surface,  when  measured,  of  about  47  square 
feet  in  most  two-column  radiators.  In  some  cases,  par- 
ticularly in  radiators  having  a  large  number  of  columns, 
the  radiators  are  very  much  overrated.  In  one  instance 
a  radiator  rated  at  36  square  feet  had  an  actual  surface 
of  only  27  square  feet.  In  purchasing  a  radiator,  there- 
fore, it  is  important  to  know  that  it  has  approximately 
the  surface  given  in  the  catalogue  of  the  manufacturer, 
as  the  radiating  power  depends  primarily  upon  the  square 
feet  of  surface  it  contains. 

Comparing  lines  2  and  6  of  Table  XV  you  will  notice 
that  the  two-column  wrought  iron  radiator  transmits 
about  20  per  cent  more  heat  than  the  two-column  cast 
iron  radiator.  This  is  undoubtedly  due  not  to  the 
difference  of  material,  but  to  the  difference  in  the  spacing 

47 


Notes         on          Heating         and         Ventilation 

of  the  columns  composing  the  radiators.  Wrought 
iron  pipe  wall  coil,  as  shown  in  the  next  to  the  last  line 
of  the  table,  condenses  almost  50  per  cent  more  steam 
than  the  cast  iron  radiator.  The  reason  for  this  is  not 


Fig.    12.      Three-Column    Cast    Iron    Radiator. 

so  much  the  difference  in  material  as  the  difference  of 
location.  In  the  case  of  the  cast  iron  radiator  the  air  at 
the  base  becomes  heated,  rises  along  the  radiator,  becom- 
ing more  and  more  heated  as  it  comes  nearer  to  the  top, 

48 


Notes 


o  n 


Heating         and         Ventilation 


so  that  at  the  top  of  the  radiator  there  is  a  smaller  dif- 
ference between  the  temperature  of  the  air  surrounding 
the  radiator  and  the  temperature  of  the  radiator  itself. 
This  reduces  the  transmission  of  heat  near  the  top  of  the 
radiator.  In  the  wall  coil,  the  sections  being  placed  in 
a  horizontal  position,  the  air  remains  in  contact  with  the 
coil  for  a  short  time  only,  so  that  the  air  surrounding  all 
portions  of  the  coil  is  practically  at  the  same  temperature. 
To  state  this  in  another  way,  in  the  'cast  iron  radiator, 
with  the  sections  placed  vertically,  the  difference  in  tem- 


Fig.    13.       Six-Column    Cast    Iron    Radiator. 


End    View    of    Sec- 
tion. 


perature  between  the  air  outside  the  radiator  and  the 
steam  inside  the  radiator  is  much  less  for  the  whole 
height  of  the  radiator  than  in  the  wall  coil,  where  the 
pipes  are  placed  horizontally,  making  the  wall  coil  much 
more  effective  per  square  foot  of  surface.  Approxi- 
mately we  can  say  that  a  wall  coil  will  do  50  per  cent 
more  per  square  foot  than  a  cast  iron  radiator.  Their 
extensive  use,  however,  excepting  in  shop  buildings,  is 
always  more  or  less  questionable,  owing  to  their  unsightly 

49 


Notes         on         Heating         and         Ventilation 

appearance   and   the   difficulty   of   installation   in   many 
places. 

Flue  Radiators — Besides  the  usual  radiator  in 
which  a  large  proportion  of  the  heat  is  given  off  by  radi- 
ation and  a  smaller  portion  by  convection,  there  is  what 
are  known  as  flue  radiators.  In  a  flue  radiator  each 
section,  as  shown  in  Fig."  14,  has  a  projecting  flange  at 
the  outer  edge,  so  that  there  is  confined  in  the  radiator 
itself  a  series  of  narrow  hot  air  flues.  In  these  radiators 
only  the  external  surface  of  the  radiator  acts  as  radiating 
surface.  The  interior  surfaces  of  the  radiator  act  as  indi- 
rect radiators  to  heat  the  air  which  is  drawn  up  from 
below  the  radiator.  Table  XVI  gives  the  loss  by  radia- 
tion from  the  radiator  as  separated  from  the  loss  due  to 
the  heat  transmitted  to  the  air  in  the  flues. 

TABLE   XVI.      HEAT   LOSS   FROM   FLUE   RADIATORS. 
2.     Rated  surface,   square  feet 42 

4.  Temperature  steam  212 

5.  Temperature  external  air 70 

6.  Difference  between  steam  and  air : 140 

7  Condensation  per  sq.  ft.  rated  surface 227 

8..  B.  T.  U.'s  per  deg.  diff.  per  sq.  ft.  rated  surface 1.57 

9.  Temperature  of  air  entering  flues 70 

10.  Temperaure  of  air  leaving  flues . 152 

11.  Cubic  feet  of  air  leaving  flues  per  minute 45.77 

12.  Average  velocity  of  air  leaving,  ft.  per  minute 171.3 

13.  Percentage  of  heat  transmitted  by  flues 45 

14.  Percentage  of  heat  radiated 55 

The  action  of  the  flue  radiator  depends  upon  the  design 
of  the  flues.  There  should  be  no  point  of  restricted  flue 
area ;  that  is,  the  air  should  be  given  a  free  passage  from 
the  base  of  the  radiator  to  the  top.  Flue  radiators  are 
particularly  serviceable  in  rapidly  circulating  the  air  in 
the  room  and  can  be  used  in  a  large  room  having  small 
window  surfaces  to  assist  in  heating  the  air  in  the  room 
more  rapidly  than  is  done  by  the  ordinary  radiator.  The 
flue  radiator  is  also  used  in  connection  with  ventilation, 
in  which  case  the  base  of  the  radiator  is  closed  and  is 

50 


Notes 


o  n 


Heating         and         Ventilation 


connected  with  the  outside  air  as  shown  in  Fig.  22, 
page  74.  This  phase  will  be  taken  up  more  in  detail 
under  the  head  of  ventilation. 

Heat  Lost  from  Radiators  Under  Varying  Tempera- 
tures.— In   the  foregoing  tables  it  has  been  assumed 


Fig.   14.     Cast   Iron   Flue   Radiator. 

that  the  heat  lost  per  degree  of  difference  of  temperature 
between  the  steam  in  the  radiator  and  the  air  outside  the 
radiator  was  a  constant  quantity.  In  general  this  may  be 

51 


Notes         on         Heating         and         Ventilation 

assumed  as  trire  for  the  ordinary  conditions  under  which 
radiators  operate.  Where  radiators  are  operated  on  very 
high  or  very  low  temperatures  there  is  a  difference  in 
the  amount  of  heat  transmitted  per  degree  of  difference 
of  temperature.  Table  XVII  gives  the  heat  transmitted 
for  each  degree  difference  of  temperature  between  the 
steam  inside  and  the  air  outside  the  radiator  per  hour 
per  square  foot  of  surface  for  the  two-column  cast  iron 
radiator  38  inches  high. 

TABLE  XVII.      HEAT   TRANSMISSION. 

Difference  in  B.  t.  u.  transmitted 

temperature.  per  deg.  diff .  per  hr. 

80  1.425 

90  1.455 

100  1.485 

110  1.515 

120  1.55 

130  1.59 

140  1.635 

150  1.665 

160  1.71 

170  1.745 

180  1.77 

190  1.815 

For  ordinary  conditions  of  operation — that  is,  when 
the  steam  is  at  from  1  to  5  pounds  pressure  and  the 
temperature  of  the  room  is  70  degrees — there  will  be  no 
necessity  to  consider  this  variation  in  the  transmission 
of  heat  due  to  differences  of  temperature  between  the 
steam  and  the  air.  There  are,  however,  conditions  in 
drying  rooms  and  similar  places  that  are  to  be  kept  at 
a  very  high  temperature,  where  this  will  make  an  ap- 
preciable difference  in  the  amount  of  radiation  to  be 
used.  In  vacuum  systems  also,  where  a  very  low 
vacuum  is  carried,  it  would  be  necessary  to  take  these 
factors  into  consideration. 

Painting  may  have  an  appreciable  effect  upon  the  heat- 
ing transmission  through  a  radiator.  The  effect  of 
painting  is  entirely  a  surface  effect,  as  the  number  of 
coats  of  painting  on  a  radiator  produce  very  little  differ- 

52 


Notes         on         Heating         and         Ventilation 

ence.  The  heat  transmission  depends  upon  the  last  coat 
put  on.  A  series  of  experiments  carried  on  recently 
showed  the  following  relative  transmission : 


TABLE  XVIII.     RELATIVE  VALUE  OF  RADIATOR  PAINTS. 


Kind  of  Surface. 

Bare  iron  surface 

Copper  bronze    

Aluminum  bronze 

Snow  White  Enamel 

No  Luster  Green  Enamel, 

Terra  Cotta  Enamel 

Maroon  Glass  Japan , 

White  Lead  Paint 

White   Zinc   Paint 


Relative  Transmission. 

1. 

76 

752 

1.01 

956 

1.038 

997 

987 


1.01 


Fig.   15. 


Installation  of  Direct  Radiators. — The  following 
suggestions  apply  to  the  placing  of  radiators  in  the  room. 
The  radiators  should  be  placed  in  the  coldesfi  portion  of 
tfie  room.  In  general  it  is  best  to  place  the  radiators  in 


Notes         on         Heating         and         Ventilation 

front  of  the  window,  selecting  a  radiator  of  such  height 
that  the  top  will  be  an  inch  or  two  below  the  window 
sill.  There  are  a  number  of  advantages  in  placing  the 
radiator  in  front  of  the  window.  Probably  the  most 
important  is  the  fact  that  it  reduces  the  strong  cold  down 
draft  along  the  window  surfaces. 

Figure  15  shows  the  effect  upon  the  circulation  of  the 
air  by  placing  the  radiator  in  front  of  the  windows.  In 
this  case  we  get  two  separate  currents  of  air.  The  cur- 
rent rising  from  the  radiator  divides,  one  current  pass- 
ing out  into  the  room,  being  cooled  by  the  wall  surfaces 
and  objects  in  the  room,  dropping  down  to  the  floor  and 
passing  back  along  the  floor  to  the  radiator;  the  other 
current,  passing  directly  to  the  cold  wall  surface,  is 
cooled,  drops  down  along  this  surface  and  comes  back 
to  the  radiator,  making  the  circulation  along  the  cold 
wajls  and  windows  close  to  the  radiator  a  local  one  which 
does  not  affect  the  occupants  of  the  room. 

Carpets  and  rugs  should  not  extend  under  the  radiator. 
If  a  radiator  is  allowed  to  stand  upon  a  carpet  or  rug 
for  any  great  length  of  time,  the  heat  from  the  legs  of 
the  radiator  will  eventually  deteriorate  the  fabric  of  the 
rug.  In  a  carpeted  room  the  radiator  may  be  placed  upon 
a  hardwood  or  a  marble  base. 

When  radiators  are  placed  next  the  wall  a  space  of  \l/2 
inches  at  least  should  be  left  for  the  circulation  of  air 
behind  the  radiator. 

Unless  otherwise  specified,  radiators  are  usually  tapped 
as  in  Table  XIX. 

TABLE  XIX.— RADIATOR  TAPPINGS. 

For  one-pipe  work  radiators   containing—  Inches. 

24  sq.  ft.  and  under 1 

From  24  to  40  sq.  ft 1% 

54 


Notes         on         Heating         and         Ventilation 

From  40  to  100  sq.   ft 1% 

Above  100  sq.  ft 2 

For  two-pipe  work  radiators  containing — 

48  sq.  ft.  and  under lx% 

From  48  to  96  sq.   ft 1^4x1 

Above  96  sq.   ft l^xl^ 

Rules  for  Direct  Heating. — The  best  method  of 
figuring  radiating  surface  is  to  determine  the  actual  heat 
loss  from  the  room  in  B.  t.  u.,  for  the  form  of 
radiator  which  you  propose  to  use.  Suppose,  for 
example,  that  a  two-column  cast  iron  radiator  is  selected. 
The  steam  pressure  to  be  carried  is  5  pounds.  The  tem- 
perature in  the  room  is  required  to  be  70  degrees.  Re- 
ferring to  the  table  of  heat  losses  from  direct  radiators 
(Table  XV),  we  see  that  a  two-column  cast  iron  radiator 
loses  1.65  heat  units  per  degree  difference  of  tempera- 
ture per  square  foot  of  rated  surface  per  hour.  The 
temperature  corresponding  to  5  pounds  pressue  of  steam 
as  given  in  Steam  Table  (Table  VI),  is  227  degrees,  and 
the  difference  between  this  and  the  temperature  of  the 
room  will  be  157  degrees.  Then  the  heat  lost  will  be 
1.65X157=259  heat  units  per  square  foot  per  hour.  Di- 
viding the  heat  loss  as  given  by  the  rule  for  loss  of  heat, 
by  259  gives  the  number  of  square  feet  of  radiation  to  be 
used. 

This  is  the  only  method  that  can  be  used  at  all  in  rooms 
where  conditions  are  exceptional.  For  rooms  of  ordi- 
nary construction,  heated  to  70  degrees,  and  an  outside 
temperature  of  0°,  a  large  number  of  thumb  rules  are 
used.  Some  of  these  thumb  rules  are  as  follows : 

In  the  following  rules  the  expression  wall  surface 
means  exposed  wall  surface,  that  is,  those  surfaces  which 
have  outside  air  temperature  on  one  side  and  room 
temperature  on  the  other  side. 

RULE  1.  Divide  the  volume  of  the  room  by  55.  Add 

55 


Notes          on          Heating         and         Ventilation 

one- fourth  of  the  exposed  wall  surface;  add  the  glass 
surface,  and  multiply  the  sum  of  these  fihree  quantities 
by  .28.  The  product  will  be  the  direct  radiation  in  square 
feet. 

RULE  2. — For  ordinary  rooms.  Divide  the  exterior 
ivaU  surface  by  4,  add  the  glass  surface  and  multiply  the 
sum  by  A, 

B. — For  entrance  hails.  Divide  the  exterior  ivall  sur- 
face by  4,  add  the  glass  surface  and  multiply  the  sum 
by  .54. 

C.-r-For  the  wall  surface  in  basement  rooms  below  the 
ground  line.  Divide  the  wall  surface  by  4  and  multiply 
the  result  by  .17. 

D. — For  floors  having  unheated  space  below.  Divide 
the  floor'space  by  4  and  multiply  the  result  by  .23. 

RULE  3.  Divide  the  volume  of  the  room  in  cubic  feet 
b\  the  factors  given  below  and  the  quotient  will  be 
the  radiating  surface  in  square  feet. 

First  floor  rooms,  two  sides  exposed: 50 

First  floor  rooms,  three  sides  expose 45 

Sleeping  rooms,  second  floor 60  fro     70 

Halls  and  bath  rooms 50 

First  floor  rooms,  one  side  exposed 55 

Offices    50  to     75 

Factories  and  stores 75  to  150 

Assembly  halls  and  churches 75  to  150 

RULE  4.  (BALDWIN'S  RULE). — Divide  the  differences 
between  the  temperature.Mt  which  the  room  is  to  be  kept 
and  that  of  the  coldest  outside  temperature  by  the  differ- 
ence betzveen  the  temperature  of  the  steam  in  the  radiator 
and  that  at  which  you  wish  to  keep  the  room  and  the  quo- 
tient will  be  the  square  feet  of  radiating  surface  to  be 
Allowed  for  each  square  foot  of  equivalent  glass  surface, 

§0 


Notes 


o  n 


Heating         and         Ventilation 


By  equivalent  glass  surface  is  meant  the  wall  surface 
divided  by  4  plus  the  glass  surface. 

In  all  of  these  rules  the  factors  to  be  allowed  for  ex- 
posure should  be  applied.  These  factors  are  given  under 
the  head  of  "Factors  for  Exposure."  Where  the  rule 
does  not  involve  the  contents  of  the  room  it  will  be  neces- 
sary in  very  large  rooms  or  in  rooms  where  the  wall 
surface  is  very  small  in  proportion  to  the  contents  of  the 
room,  to  add  a  certain  proportion  of  radiation,  usually 
not  more  than  20  per  cent,  to  allow  for  heating  the  air 
in  the  room  quickly  when  it  has  once  been  allowed  to 
cool. 

Example  (Direct  Radiation). — Tn  order  to  under- 
stand better  the  methods  of  determining  the  heating 
surface  required  for  a  given  .house,  it  would  *be  best  to 
consider  a  concrete  example.  Figs.  Ifi,  17  and  18  reore- 
sent  the  basement,  first  and  second  floors  of  a  residence. 
The  house  is  constructed  of  wood,  sheathed,  papered  and 
clap-boarded  on  the  outside  and  plastered  on  the  inside. 
On  the  first  floor  the  rooms  are  9  feet  6  inches  high  and 
on  the  second  floor  8  feet  6  inches  high.  The  windows 
are  6  feet  high  and  the  standard  size  is  3  feet  wide. 
Table  XX  gives  the  general  dimensions  of  the  room  and 
the  heat  losses  from  the  various  rooms,  assuming  the 
temperature  of  the  outside  air  to  be  zero  and  the  tem- 
perature of  the  inside  to  be  70  degrees. 

TABLE  XX.— DIMENSIONS'  AND   HEAT  LOSSES. 


Room.                      Dimensions.  Volume. 

Parlor    13'9"xl2'9"x9'6"  1,665 

Sitting  room 14'3"xl5'6"x9'6"  2,100 

Dining  room 12'6"xl3'9"x9'6"  1,640 

Kitchen     13'0"xl3'0"x9'6"  1,610 

Hall    12'9"xlO'0"x9'6"  1,210 

S-econd  Floor. 

W.  chamber Il'6"xl3'6"x8'6"  1,320 

67 


B.t.u. 
Lost 

Wall      Window    Per 

Surface.  Surface.  Hour. 

216  36  9,450 

95  48  7,035 

145  36  7,350 

249  36  10,300 

197  18  7,035 

172  48          10,050 


Notes         on         Heating         and         Ventilation 

Alcove  10'0"x  9'6"x8'6"  810  130            40            7,560 

So.   chamber 12'6"xl4'9"x8'6"           ,1,560  172  24             7,035 

N.    chamber 13'     x!3'  x8'6"           1,440  188             24             7,455 

Bath   6'     x  8'  xS'6*              410  50          ^18             3,150 

E.  chamber. .....13'     x  8'  x8'6"             880  160            18            5,250 

Front   hall.. 14'     x  4'  x8'6"              885  33             18             2,730 

8'     x  6'  x8'6" 

TABLE  XXI.— RESULTS  OF  COMPUTATION,   DIRECT  SYSTEM. 

Radiating 

B.t.u.  B.t.u.  Surface.  Two      Radiating 

from  Corrected  for  Column  Cast          Surface 

Table  XXI.  for  Exposure.  Iron  Sq.  Ft.         by  Rule  3. 

First  Floor. 

Parlor   9,450  10,395  39                      33.5 

Sitting    room..     7,035  7,035  27                      38 

Dining  room...     7,350  8,085      •  .            30                      30 

Kitchen  10,300  10,300  39                      32 

Hall    7,035  7,770  29                       24 

Second  Floor.  , 

W.  chamber...  10,050  11,055  42                      22 

Alcove 7,560  8,316  31                       13 

S.  chamber....     7,035  7,035  27                      26 

N.  chamber....     7,455  8,190  31                      2*       . 

Bath     -.150  3,465  13                         'i 

E.    chamber...     5,250  5,250  20                      14.7 

Halls    2,730  3,003  12                       14.7 

The  method  used  in  determining  the  British  thermal 
units  lost  from  the  room  is  as  follows :  In  Table  XII  a 
wall  constructed  as  described  loses  .25,  Table  XI  gives 
the  loss  from  the  glass  surfaces  as  1.03.  Then  multiply- 
ing the  wall  surface  by  .25  will  give  the  B.  t.  u.  lost 
per  square  foot  per  degree  difference  and  each  square 
foot  of  glass  surface  loses  about  one  B.  t.  u.  per  square 
foot.  Take,  for  example,  the  parlor.  The  wall  surface 
is  216  square  feet.  Multiply  this  by  .25 ;  the  result,  54 
B.  t.  u.  lost  per  square  foot  per  degree  difference  of 
temperature.  Add  the  loss  from  the  glass  surface,  36  B. 
t.  u.,  makes  a  total  loss  of  90  B.  t.  u.  Multiply- 
ing this  by  the  difference  between  the  outside  and  the 
inside  temperature,  gives  the  heat  lost,  or  90X70=6,300 
B.  t.  u.  lost  from  the  room  per  hour.  To  this  must 
be  added  the  loss  through  the  wall  by  leakage  which  has 
been  assumed  to  be  50  per  cent,  making  the  total  loss 
9,450  B.  t.  u. 

In  Table  XXI  the  second  column  gives  the  B.  t.  u. 

58 


Notes 


on         Heating         and         Ventilation 


as  determined  in  Table  XX;  the  third  column  the  B.  t. 
u.  corrected  for  exposure,  10  per  cent  being  added  to 
rooms  having  north  and  west  exposures,  as,  in  this  case, 
the  prevailing  winds  are  from  the  west.  Column  4  gives 


Fig.    16.      Basement.  Plan. 


the  radiating  surface  required  to  heat  the  rooms  with  a 
two-column  cast  iron  radiator.  Column  5  gives  the 
radiating  surface  as  determined  by  Rule  3. 


59 


Notes 


o  n 


Heating          and          Ventilation 


The  quantities  in  column  4  are  obtained  in  the  fol- 
lowing manner.  The  steam  pressure  to  be  carried  in  the 
radiator  is  5  pounds.  The  corresponding  temperature 


Fig.    17.       First    Floor. 

of  steam  is  227  degrees.  The  temperature  of  the  room 
is  70  degrees.  The  difference  in  temperature  between  the 
rpom  and  the  stearq  will  be  157  degrees.  In  the  last 

00 


Notes 


o  n 


Heating          and          Ventilation 


column  of  Table  VII  the  heat  lost  for  a  two-column  cast 
iron  radiator  is  given  as  1.05  B.  t.  u.  per  degree  differ- 
ence per  hour.  Then  the  total  heat  lost  per  square  foot 
per  hour  will  be  157X1-05=260  B.  t.  u.,  that  is,  each 
square  foot  of  radiator  surface  will  give  to  the  room 


Fig.   18.     Second   Floor. 

260  heat  units  per  hour.  Dividing  the  heat  lost  from 
the  room,  as  given  in  column  3,  by  260,  will  give  the 
results  shown  in  column  4. 

In   column   5   the-  radiating  surface  has  been   deter- 
mined by  Rule  3,  which'  is  sometimes  called  the  Volume 

61 


Notes         on          Heating         and         Ventilation 

Rule ;  that  is,  the  cubic  contents  of  the  rooms  are  divided 
by  a  certain  factor,  depending  upon  the  location  of  the 
room.  A  careful  comparison  of  columns  4  and  5, 
together  with  an  inspection  of  the  plans,  will  show  the 
inconsistency  of  the  volume  rule.  The  volume  rule  can 
be  used  only  where  the  room  has  an  average  amount  of 
cubic  contents,  as  compared  with  its  wall  surface.  To 
get  the  best  results  it  is  better  to  employ  the  method 
that  has  been  used  in  determining  the  results  in  column  4. 
The  case  often  arising  where  a  contractor  guarantees 
to  heat  a  building  to  70°  when  the  outside  temperature  is 
zero.  When  the  plant  is  finished  the  temperature  out- 
side is  many  degrees  above  zero.  What  temperature 
should  the  rooms  heat  to  under  this  higher  outside  tem- 
perature in  order  to  have  the  room  heat  to  70°  in  zero 
weather? 

Assume  t^temperature  of  the  outside  air  from  con- 
tract conditions  usually  0°. 

t2— temperature  of  air  in  the  room  which  was 
guaranteed  by  contractor. 

t3— temperature  of  steam  in  the  radiator  during 
test. 

t4=actual  temperature  outside  air  during  test. 

t5= computed  temperature  of  room  for  test  con- 
ditions. 
The  heat  loss  from  the  room  under  contract  conditions 

is  W 

-+G     n(t2-tl)  (1) 

4 
Heat  loss  from  room  under  test  conditions  is 

W 

+G     n(t5-t4)  (2) 


62 


Notes          on          Heating          and          Ventilation 

Heat  loss  from  radiator  under  contract  conditions  = 
(t3~t2)c  (3) 

where    c    is    coefficient    of    transmission.      Heat    loss 
from  radiator  under  test  conditions  = 

(ta— tB)c  (4) 

Then  equation   (1)   must  equal  (3)   and  equation   (2) 
must  equal   (4),  hence 

|-G^n=-- —  and  (5) 

4  /  t2— t, 

W          x          (t3— r)c 
-+G)n=-  (6) 

4  /  t5-t4 

Equating-  the  right-hand  member  of  equations  (5) 
and  (6)  we  have 

ts— t2       ts— 15 

t2— tt       t5— 14 
Assuming  tt=0°   and  t2=70°   and  solving  for  t5 

t5=.695t4+70°  (8) 

The  following  Table  XXII  has  been  computed  from 
equation  8  and  shows  the  room  temperature  for  dif- 
ferent outside  temperature  with  the  same  radiation  in 
the  room  and  the  same  steam  temperature. 

TABLE  XXII. 

Room   Temperature  Corresponding  to  Temperature  of  Outside  Air. 

Temperature  of  Temperature  of  room  Temperature  of  room 

outside  air.  2-column  radiator.  3  column  radiator 

—30  52  53 

—20  58  59 

—10  64  64 

0  70  70 

10  77.5  75 

20  83  83 

30  90  89 

40  97  95 

50  103.5  105.5 

60  110  108 

70  117  115 

80  123.5  121.5 

90  130  128 

100  137  134.5 

63 


Notes         on          Heating         and         Ventilation 

Table  XXII  shows  the  temperature  that  should  be 
obtained  in  a  room  for  various  outside  temperatures, 
the  original  guarantee  being  to  heat  the  house  to  70 
degrees  in  zero  weather. 

Transmission  of  Heat  Under  Various  Conditions. — 
The  German  engineers  use  the  following  method  of  cal- 
culating the  amount  of  heat  which  will  pass  through  a 
square  foot  of  heating  surface  per  hour.  Assume  H  to 
be  the  total  heat  transmitted  per  hour;  t  the  difference 
between  the  average  temperature  of  the  hot  and  cold 
fluids ;  c  a  constant  depending  upon  the  kind  of  surface, 
the  hot  fluid  and  the  cold  fluid  and  let  a  equal  the  area 
of  the  surface.  Then 

H  ==  c  t  a. 

Rietschel  gives  the  following  values  for  the  heat  trans- 
mitted :  c 
From   air   or   smoke   through   a   clay  plate 

about  y%  inch  thick  to  air 1.00 

From  air  .or  smoke  through  a  cast  or  sheet 

iron  plate  to  air 1.4  to      2.0 

From  air  or  smoke  through  a  cast  or  sheet 

iron  plate  to  water  or  the  apposite.  ...     2.6  to      4.0 
From  steam  through  cast  iron  or  wrought 

iron  plate  to  air 2.2  to      3.6 

From  steam  through  a  metal  wall  to  water.  160.0  to  200.0 


64 


CHAPTER  IV. 

Design  of  Indirect  Steam  Heating  System. — It  is 
seldom  that  indirect  radiators  only  are  installed.  This 
is  due  chiefly  to  the  increased  cost  of  installation  and 
operation  of  such  a  plant,  as  compared  with  a  plant 
using  both  direct  and  indirect  radiation.  In  a  resi- 
dence heated  by  indirect  radiation  alone,  it  will  be 
necessary  to  introduce  an  excess  of  air  over  that  re- 
quired by  ventilation.  This  materially  increases  the 
cost  of  operation.  In  designing  an  indirect  heating 
plant  the  loss  of  heat  from  the  building  is  figured  in 
the  same  way  as  with  the  direct  system.  In  using  indi- 
rect radiation  alone  it  will  be  necessary  to  introduce 
enough  air  so  that  the  heat  left  in  the  room  will  be  suf- 
ficient to  take  .care  of  the  losses  from  the  walls  and  win- 
dows. In  order  to  determine  the  amount  of  surface  to 
be  placed  in  the  room,  it  is  necessary  to  know  the  tem- 
perature to  which  the  radiator  will  heat  the  air  and  the 
amount  of  heat  given  off  by  the  indirect  radiator  under 
different  conditions  of  operation. 

Heat  Lost  from  Indirect  Steam  Radiators. — The 
amount  of  heat  that  may  be  obtained  from  a  given  indi- 
rect radiator  will  depend  upon  the  temperature  at 
which  the  air  is  taken  in,  the  temperature  of  the  radi- 
ator, and  the  cubic  feet  of  air  passing  through  the 
radiator.  The  following  table  gives  the  relation  be- 
tween the  above  quantities,  assuming  the  temperature 
of  the  air  entering  the  radiator  to  be  zero,  the  tempera- 
ture of  the  steam  in  the  radiator  227  degrees,  the  tem- 
perature corresponding  to  5  pounds  gauge  pressue : 

In  school  buildings  and  in  buildings  where  the  flues 

65 


Notes 


o  n 


Heating          and          Ventilation 


are  of  ample  size  the  amount  of  air  passing  per  square 
foot  of  radiating  surface  may  be  assumed  to  be  200 
cubic  feet  per  hour.  In  residences  and  buildings  where 
the  flues  are  usually  small,  the  amount  of  air  passing 


Fid.  19.     Extended  Surface  Indirect  Radiator. 

per  square  foot  of  surface  per  hour  does  not  exceed  150 
cubic  feet. 

From  the  results  of  the  tests  on  indirect  radiators 
given,  the  following  points  may  be  noted : 


Fig.  20.      Long   Pin   Indirect   Radiator. 

If  the  temperature  of  the  air  entering  the  radiator 
is  constant,  then  the  temperature  of  the  air  leaving 


66 


Notes         on          Heating         and         Ventilation 

the  radiator  will  decrease  as  the  amount  of  air  passing 
through  the  radiator  is  increased. 

In  order  to  determine  thev  amount  of  heat  trans- 
mitted by  the  radiator  it  is  necessary  to  assume  the 
number  of  cubic  feet  of  air  that  will  pass  through  the 
radiator  per  square  foot  of  radiation.  You  will  also 
note  the  difference  between  the  extended  surface 
radiator  and  the  long  pin  radiator  (Fig.  20).  As 
shown  in  Table  XXIII,  the  temperature  at  which 
the  air  is  heated  by  the  long  pin  is  less  than  the  tem- 
perature to  which  the  air  is  heated  by  the  short  pin 
with  the  same  quantity  of  air  passing.  This  is  un- 
doubtedly due  to  the  fact  that  the  pins  are  so  long 

TABLE   XXIII.     HEAT   LOSSES   FROM  INDIRECT  RADIATORS. 


B.    t.    u.    trans- 

mitted per  sq.  ft. 

Cubic   feet 

Increase  in 

of  radiation  per 

of  air 

temperature 

Pounds    of 

degree    diff.     In 

passing 

of  the  air 

steam  con- 

temper,    of    air 

per  sq.   ft. 

passing 

densed  per 

passing  through 

of 

the 

sq.    ft.    of 

radiator  and  the 

radiation. 

radiator. 

radiation. 

steam. 

Stan- 

Stan- 

Stand- 

dard 

Long 

dard 

Long 

dard         Long 

Pin. 

Pin. 

Pin. 

Pin. 

Pin.            Pin. 

50 

,  147 

140 

.125 

.15 

.80                 .95 

75 

148 

137 

.17 

.21 

1.17               1.27 

100 

,  140 

135 

.24 

.26 

1.51               1.60 

125 

,  138 

132 

.295 

.31 

1.85               1.90 

150 

135 

129 

.355 

.36 

2.22               2.20 

175 

132 

126 

.41 

.405 

2.57              2.47 

200 

130 

123 

.47 

.45 

2.90               2.72 

225 

127 

120 

.53 

.49 

3^25               3^00 

250 

123 

118 

.585 

.53 

3.60               3.20 

275 

121 

115 

.645 

.57 

3  90               S  40 

300. 

119 

112    >   •:-'• 

.700 

.61 

4.22               3*.  60 

that  the  ends  become  cooled.  On  the  other  hand,  the 
long  pin  type  is  a  very  desirable  type  to  use  when  one 
wishes  to  pass  large  quantities  of  air,  as  the  radiator 
has  ample  air  passage.  This  is  primarily  the  work  for 
which  it  is  designed.  The  short  pin  gives  better  results 
for  ordinary  houses  where  small  quantities  of  air 
pass  through  the  radiator. 

67 


Notes         on          Heating         and         Ventilation 

Installation  of  Indirect  Radiators. — Indirect  radi- 
ators are  placed  in  a  chamber  or  box,  usually  situated 
in  the  basement  of  the  building,  as  close  as  possible 
to  the  vertical  flue  leading  to  the  room  .which  they 
are  to  heat.  The  air  is  admitted  to  the  radiator  by  a 
duct  or  flue,  connected  with  the  outside  air.  This  duct 
should  be  supplied  with  a  suitable  damper  and,  if  pos- 
sible, be  so  arranged  as  to  close  automatically  when 
the  steam  pressure  is  taken  off  the  radiator.  The  cold 
air  is  usually  admitted  directly  beneath  the  radiator 
and  the  heated  air  on  leaving  the  room  is  taken  off 
at  one  side. 

TABLE   XXIV.      INDIRECT    RADIATORS— TEMPERATURES    OF 
LEAVING  AIR. 

Temperature  of  air  Temperature  of  air 

Temperature                        leaving  the  radiator  leaving  the  radiator 

of  air  enter-                        with    a   velocity   of  with    a   velocity  of 

ing  the  radl-                         200    cu.    ft.    of    air  150    cu.    ft.    of    air 

ator.                                         per  sq.   ft.   surface.  per  sq.   ft.   surface. 

Standard          Long  Standard            Long 

Pin                  Pin  Pin                 Pin 

0 130                     125  135                     128 

10 134                     128  139                     132 

20 139                     132  144                     136 

30 144                     136  149                     140 

40 148                     141  153                     144 

50 153                     144  158                     146 

The  casing  surrounding  indirect  radiators  is  usually 
built  of  galvanized  iron  and  it  should  be  bolted  to- 
gether with  stove  bolts,  so  that  the  casing  may  be 
easily  removed.  A  much  better  method,  but  one 
which  is  more  expensive,  is  to  enclose  the  radiator 
in  a  small  brick  chamber  with  cement  floor.  This 
chamber  should  be  large  enough  so  that  the  radiator 
is  accessible  for  repairs.  Sometimes  a  duct  is  pro- 
vided in  the  radiator  casing  so  that  cold  air  may  be 
taken  around  the  radiator  and  mixed  with  the  heated 
air  through  a  suitable  damper,  controlled  from  the 
room  which  is  heated.  This  is  a  very  common  ar- 

68 


Notes         on         Heating         and         Ventilation 


rangement  in  school  buildings.     Fig.  21  shows  a  sketch 
of  an  arrangement  of  this  kind. 

The  pipes  or  ducts  leading  from  an  indirect  radi- 


Fig.   21. 


Notes          on          Heating          and          Ventilation 

ator  should  be  carried  to  the  room  as  directly  as 
possible.  It  is  better  to  have  a  long  cold  air  pipe 
than  a  short  hot  air  pipe.  A  long  horizontal  hot  air 
pipe  should  be  avoided.  Where  the  air  from  the 
indirect  radiator  is  to  be  used  primarily  for  ventila- 
tion it  is  best  to  place  the  hot  air  register  near  the 
ceiling. 

The  indirect  radiators  are  usually  suspended  in  the 
radiator  chamber  on  iron  pipes  supported  by  rods 
hanging  from  the  ceiling.  There  should  be  at  least  10 
inches  clear  space  between  the  radiator  and  the  bot- 
tom and  top  of  the  casing.  The  casing  of  the  radi- 
ator should  fit  the  radiator  as  closely  as  possible,  so 
that  very  little  air  is  allowed  to  pass  around  the  radi- 
ator without  being  heated.  Indirect  radiators  should 
be  placed  at  least  2  feet  above  the  water  line  of  the 
boiler,  if  they  are  to  be  operated  on  a  gravity  system 
of  circulation,  and  should  be  so  arranged  that  the 
condensed  water  will  drain  from  them  without  trap- 
ping. The  tappings  of  these  radiators  are  the  same  as 
for  double  pipe  direct  steam  radiators.  The  following 
table  gives  the  general  proportions  for  an  indirect  ra- 
diator system: 

TABLE  XXV.— SIZE  OF  FLUES  FOR  INDIRECT  RADIATOR. 


Heating 
Surface, 
Sq.  Ft. 
20  

Area  of  Cold 
Air  Supply, 
Sq.  In. 
.  30 

Area  of  Hot 
Air  Supply, 
Sq.  In. 
40 

Size  of 
Brick  Flue  for 
Hot  Air. 
8x  8 

Size  of 
Register. 
8x  8 

30 

45 

60 

8x12 

8x12 

40 

60 

80 

8x12 

10x12 

50  

75 

100 

12x12 

10x15 

60  

90 

120 

12x12 

12x15 

80  

120 

160 

12x16   n±6 

14x18 

100 

150 

200 

12x20  ~"  L 

16x20 

120 

180 

240 

14x20 

16x24 

140  .. 

..210 

280 

16x20 

20x24 

Heating  Effect  of  an  Indirect  Radiator. — It  is  usual 
to   assume   that   the   air   enters   the   radiator   at   zero 


76 


Notes          on          Heating          and          Ventilation 

degree  of  temperature,  in  which  case  it  will  leave  the 
radiator  at  about  130  degrees,  the  steam  pressure  in 
the  radiator  being  5  pounds  and  the  velocity  through 
the  radiator  being  200  cubic  feet  per  hour  per  square 
foot  of  radiator.  Under  the  above  conditions  an  ordi- 
nary pin  radiator  will  give  off  470  B.  t.  u.  per 
square  foot,  or,  say  approximately,  450  B.  t.  u. 
Under  these  conditions  the  air  entering  the  room  will 
be  at  a  temperature  of  130  degrees,  and  if  the  tempera- 
ture of  the  room  is  70  degrees  this  air  will  be  capable 
of  losing  to  the  room  60  degrees,  or,  in  other  words, 
there  is  60  degrees  of  temperature  available  in  this 
air  for  heating  purposes,  or  of  450  B.  t.  u.  given  out 
by  the  radiator  210  B.  t.  u.  are  available  for  heating  the 
room. 

SOME  RULES  FOR  INDIRECT  HEATING. 

RULE  1. — For  ordinary  rooms.  Divide  the  wall  sur- 
face by  4,  acid  the  glass  surface,  and  multiply  the  sum  by 
.6.  The  quotient  urill  be  the  amount  of  indirect  radiation 
necessary  to  heat  the  room. 

B. — For  entrance  halls.  Divide  the  exterior  ivall  sur- 
face by  4,  add  the  glass  surface  and  multiply  the  sum  by 
.75,  the  product  will  be  the  number  of  square  feet  of  indi- 
rect radiation. 

RULE  2. — Figure  the  heating  surface  the  same  as  for 
direct  heating.  Add  40  per  cent. 

RULE  3. — Divide  the  volume  of  the  room  by  40.  The 
quotient  is  the  square  feet  of  indirect  surface  required  to 
heat  the  rooms  on  the  first  floor.  For  second  and  third 
floor  rooms  divide  by  50,  and  in  stores  and  large  rooms 
divide  by  60. 

Example  of  Indirect  Heating. — Take  the  same  house 

71 


Notes          on          Heating          and          Ventilation 


that  was  used  in  the  problem  for  direct  heating.  In  this 
case  all  rooms  are  to  be  heated  by  indirect  radiation.  It 
is  in  actual  practice  an  unusual  arrangement,  but  it  is  fig- 
ured out  in  this  way  as  an  illustration  merely. 

The  heat  loss  in  this  house  will,  of  course,  be  the  same 
in  both  direct  and  indirect  heating  and  is  given  in  Table 
XXI  (p.  58).  Assume  that  the  air  enters  the  radiator 
at  zero  degrees  and  leaves  at  130  degrees;  that  the  steam 
in  the  radiator  is  at  5  pounds  pressure  and  that  200  cubic 
feet  of  air  is  passed  through  the  radiator  per  square  foot 
of  surface.  From  the  results  determined  in  paragraph 
headed  "Heating  Effect  of  the  Indirect  Radiator"  each 
square  foot  of  radiation  gives  approximately  450  B.  t. 
u.  If  the  temperature  of  the  room  is  70  degrees  only 
60  degrees  of  the  heat  given  to  the  air  is  effective  in  heat- 
ing the  room.  As  the  total  amount  of  increase  in  tem- 
perature is  130  degrees,  only  approximately  60-^-130,  or 
45  per  cent,  is  available  for  heating.  Each  square  foot 
of  indirect  radiation  gives  off  .450  B.  t.  u.,  45  per  cent 
of  450,  or  200  B.  t.  u.,  will  be  available  for  heating 
the  room.  The  heat  loss  as  given  in  the  table  for  the 
parlor  is  10,395  B.  t.  u.  Dividing  this  by  200  gives 
52,  the  number  of  square  feet  of  radiation  required  for 
the  room. 

TABLE  XXVI.- 


-RESULTS  OF  COMPUTATION,   INDIRECT 
STSTEM. 


B.   t.   u. 

Lost 
Per  Hour. 

First  Floor — 

Parlor   10,395 

Sitting  room 7,035 

Dining  room. . . .  8,085 

Kitchen    10,300 

Hall,  2d  floor.  ..15,800 

Second  Floor — 
W.   chamber, 

alcove     19,370 

So.   chamber 7,035 

N.    chamber....  8,190 

Bath 3,465 

E,  chamber 5,250 


Size  of 

Volume 

Radiator 

Area  Hot 

Area 

of 

in.  Sq.  Ft. 

Air  Flue. 

Vent  Flue. 

Room. 

50 

100 

12x12 

900 

35 

70 

8x12 

700 

40 

80 

8x12 

720 

50 

100 

12x12 

1,000 

73 

145 

12x12 

1,500 

93 

180 

12x20 

1,600 

35 

70 

8x12 

700 

40 

80 

8x12 

750 

17 

40 

6x  8 

800 

24 

50 

6x  8 

600 

Notes          on          Heating         and         Ventilation 

Size  of  Hot  Air  Pipe. — Fifty-two  square  feet  of 
radiation  passing  240  cubic  feet  of  air  per  square  foot 
will  pass  12,480  cubic  feet  of  air  per  hour ;  12,480  is  3.47 
cubic  feet  per  second.  Allowing  a  velocity  of  5  feet 
per  second,  the  area  of  the  hot  air  pipe  is  3.47^-5=. 69 
square  feet.  This  equals  99  square  inches,  which  is  the 
proper  arfea  of  the  pipe.  The  size  of  the  cold  air  pipe 
leading  to  yie  radiator  is  usually  made  the  same  size  of 
the  hot  air  pipe.  Table  XXVI  gives  the  results  for  the 
whole  house  \computed  in  the  same  manner  as  given 
above.  In  the  table  the  odd  figures  and  decimals  have 
been  left  off. 

In  selecting  the  size  of  radiator  for  a  room,  it  is  neces- 
sary to  select  those  that  vary  by  10  square  feet  or  more, 
as  indirect  radiator  sections  are  not  made  smaller  than 
10  square  feet  per  section.  In  a  house  where  the  radi- 
ators would  be  less  than  three  sections,  it  is  necessary  to 
put  two  or  three  rooms  on  the  same  radiator,  as  it  is  not 
desirable  to  make  very  small  indirect  stacks.  There  is 
always  danger,  however,  in  taking  the  heat  for  two  sep- 
arate rooms  off  the  same  radiator,  that  the  heat  will  not 
distribute  equally  between  the  two  rooms.  When  sep- 
arate rooms  are  heated  from  the  same  radiator,  care 
should  be  taken  to  see  that  pipes  leading  to  the  two 
rooms  have  about  the  same  length  and  as  nearly  as  pos- 
sible the  same  resistance. 

Combination  of  Direct  and  Indirect. — A  much  more 
common  arrangement  of  indirect  radiators  is  to  put  in 
just  enough  indirect  radiation  to  give  the  proper  amount 
of  air  for  ventilation  and  supply  the  additional  heat  for 
the  room  with  direct  radiation.  Each  system  is  installed 
as  though  the  two  were  separate,  except  that  they  take 

73 


Notes 


o  n 


Heating         and          Ventilation 


their  steam  from  the  same  steam  mains  and  return  into 
the  same  return  pipes.  In  this  system  the  direct  radi- 
ators can  be  installed  on  the  one-pipe  system,  but  the  in- 
'direct  should  be  installed  on  the  two-pipe  system,  as  in- 
direct radiation  does  not  work  well  on  a  one-pipe  system. 


Fig.  22.      Arrangement  of  Flue   Radiator. 

It  is  not  necessary  to  put  indirect  radiation  into  all  the 
rooms  of  a  residence.  They  are  put  into  the  princpial 
living  rooms,  the  hall  and  the  large  bedrooms.  Where 
the  house  is  small  it  may  be  necessary  to  put  indirect  ra- 
diation only  in  the  sitting  room  and  in  the  hall.  An  ex- 

74 


Notes          on          Heating         and         Ventilation 

ample  of  this  kind  will  be  taken  up  under  the  head  of 
ventilation. 

Flue  Radiators. — Where  only  a  small  quantity  of 
air  is  needed  for  ventilation  flue  radiators  may  be  used  in 
place  of  indirect  radiators  as  shown  in  figure  22. 

The  damper  in  the  outside  wall  regulates  the  amount  of 
air  passing  into  the  room  and  in  extremely  cold  weather 
this  may  be  entirely  closed.  Table  XVI  on  page  50  shows 
the  heat  loss  from  this  type  of  radiation  and  the  amount 
of  air  that  the  flues  will  pass.  In  figuring  this  type  of 
radiation  figure  the  same  as  for  direct  radiation  and  add 
25%.  Each  30  square  feet  of  flue  radiation  will  furnish 
ventilation  sufficient  for  one  person. 


75 


CHAPTER  V. 

STEAM  BOILERS. 

Types. — Boilers  are  divided  into  two  general  classes 
—fire  tube  or  tubular,  and  water  tube  or  tubulous  boilers. 
The  commonest  form  of  boiler  used  for  heating  purposes 
in  this  country  is  what  is  known  as  the  return  flue  fire 
tube  boiler.  These  boilers  are  adapted  to  plants  of  over 
30  and  under  150  horsepower  and  where  the  pressure 
does  not  exceed  100  pounds.  For  pressures  above  100 
pounds  it  is  customary  to  use  water  tube  boilers.  There 
is  one  exception,  that  is  the  Scotch  marine  boiler,  which 
is  a  fire  tube  boiler  and  which  can  be  made  to  with- 
stand pressures  of  200  pounds  and  over  in  large  sizes, 
as  in  this  boiler  the  fire  does  not  come  in  contact  with 
the  outside  shell. 

For  heating  purposes  there  have  been  introduced  a 
number  of  special  forms  of  boiler,  a  great  many  of  these 
forms  being  built  of  cast  iron.  Cast  ^iron  boilers  are  not 
usually  operated  at  pressures  exceeding  10  pounds. 

Any  of  these  forms  of  boilers  may  be  used  for  heat- 
ing, the  selection  and  the  proper  form  will  depend  upon 
the  conditions  in  each  particular  case.  In  selecting  a 
boiler  the  following  points  should  be  taken  into  consid- 
eration :  The  boiler  must  be  of  sufficient  strength  to 
withstand  the  maximum  pressure  to  be  carried.  This 
does  not  usually  exceed  10  pounds.  It  must  have  suffi- 
cient heating  surface  in  proportion  to  the  grate  surface 
to  be  economical.  The  stack  temperature  in  a  low  pres- 
sure boiler  should  not  exceed  500  degrees.  The  boiler 
must  have  sufficient  liberating  surface  so  that  the  steam 
formed  in  the  water  may  escape  from  the  surface  of  the 

7$ 


Notes         on          Heating         and         Ventilation 

water,  without  carrying  a  large  quantity  of  water  with  it. 
The  boiler  must  have  large  circulating  areas  so  that  the 
water  may  be  circulated  freely  to  the  heating  surfaces 
and  the  steam  formed  may  pass  away  from  the  heating 
surfaces  without  restrictions.  The  steam  that  forms  on 
the  heating  surfaces  rises  in  bubbles  and  is  liberated  from 
the  surface  of  the  water.  If  the  boiler  has  insufficient 
liberating  surfaces  or  the  circulating  areas  are  contracted 
the  steam  cannot  rise  rapidly  enough  and  bubbles  of 
steam  remain  on  the  heated  surfaces.  These  bubbles  pre- 
vent the  water  from  reaching  the  heating  surfaces  and  as 
steam  is  a  poor  conductor  of  heat  this  results  in  an  over- 
heating of  these  surfaces.  This  trouble  may  be  very 
serious,  especially  in  the  water  tube  type  of  boiler,  and 
results  in  the  burning  out  of  the  tubes.  In  cast  iron 
boilers  the  lack  of  proper  liberating  surfaces  and  suffi- 
cient steam  space  often  causes  excessive  priming.  The 
question  of  circulating  area  and  liberating  surface  is  of 
more  importance  in'  a  low  pressure  boiler  plant  than  in  a 
high  pressure  plant,  as  steam  at  5  pounds  pressure  has 
about  six  times  the  volume  of  steam  at  100  pounds  pres- 
sure ;  so  that  to  have  relatively  the  same  circulating  area 
and  liberating  surface  in  a  low  pressure  boiler,  we  should 
have  five  times  as  much  as  in  a  high  pressure  boiler. 

In  boilers  for  heating  purposes  it  is  desirable  that  they 
should  have  sufficient  steam  space,  and  a  large  storage  of 
water,  particularly  if  the  plant  is  to  be  continuously  oper- 
ated. In  boilers  having  large  water  storage  it  is  possible 
to  maintain  a  steam  pressure  on  the  boiler  all  night  un- 
der banked  fires.  Where  boilers  are  to  be  operated  only 
occasionally,  it  may  be  desirable  to  have  a  small  quanti- 
ty of  water,  as  each  time  the  boiler  is  started  it  is  nec- 
essary to  heat  all  the  water  in  the  boiler  before  steam  is 

77 


Notes         on         Heating         and         Ventilation 

formed.  The  ordinary  fire  tube  return  flue  boiler,  on  ac- 
count of  its  large  water  storage,  liberal  circulating  areas 
and  large  liberating  surface,  is  a  desirable  one  for  heat- 
ing purposes  in  large  buildings. 

Proportion  of  Boilers. — The  heating  surfaces  in  a 
boiler  are  those  surfaces  which  have  water  on  one  side 
and  hot  gases  on  the  other.  A  boiler  should  be  so  pro- 
portioned as  to  transmit  as  much  of  the  heat  generated 
by  the  fuel  to  the  water  as  possible.  Experience  has  de- 
termined that  for  best  results  in  boilers  of  50  horse- 
power and  over  a  square  foot  of  heating  surface  should 
evaporate  not  more  than  three  pounds  of  water  per 
square  foot  of  heating  surface.  For  small  houses,  where 
heating  boilers  of  but  a  few  horsepower  are  used,  it  is 
not  usual  to  allow  a  square  foot  of  heating  surface  to 
evaporate  more  than  2  pounds  of  water  and  when  a 
square  foot  of  heating  surface  evaporates  more  than  the 
amounts  given  above,  the  transmission  of  heat  through 
the  plate  becomes  so  rapid  that  all  the  heat  is  not  re- 
moved; the  result  is  an  excessively  high  stack  tempera- 
ture and  a  corresponding  loss  of  heat.  Surfaces  that 
have  steam  on  one  side  and  hot  gases  on  the  other  are 
called  superheating  surfaces.  It  is  not  advisable  to  have 
superheating  surfaces  in  a  boiler. 

Small  heating  boilers  are  distinctly  different  from 
power  boiler  or  heating  for  large  plant.  In  large 
plants  coal  is  being  fed  to  the  boiler  almost  continu- 
ously and  the  flues  are  carrying  a  large  quantity  of 
gases.  Small  house  heating  boilers  are  fed  at  infre- 
quent intervals  and  the  flues  of  these  boilers  do  very 
little  of  the  work  of  transmitting  heat.  In  small  boil- 
ers a  distinction  must  be  made  between  the  flue  sur- 
face and  the  fire  surface.  The  fire  surfaces  are  those 

78 


Notes          on          Heating          and          Ventilation 

heating  surfaces  upon  which  the  rays  of  radiant  heat 
from  the  fire  impinge  directly.  During  the  periods 
-/hen  the  drafts  are  closed  most  of  the  steaming  in 
the  boiler  is  produced  by  the  fire  surface,  it  is  there- 
fore important  in  a  house  heating  boiler  to  have  a 
large  amount  of  fire  surface  as  compared  with  the  flue 
surface.  It  is  good  practice  to  have  60  per  cent  fire 
surface  and  40  per  cent  flue  surface  in  cast-iron  house 
heating  boilers. 

The  proportion  of  grate  surface  to  heating  surface 
depends  upon  the  kind  of  fuel  and  the  intensity  of 
the  draft.  In  small  boilers  used  for  heating  purposes 
it  is  usual  to  allow  one  square  foot  of  grate  surface  to 
every  15  to  30  square  feet  of  heating  surface.  For 
boilers  50  horsepower  and  over  it  is  usual  to  allow 
from  30  to  40  square  feet  of  heating  surface  per  square 
foot  of  grate  surface  and  in  very  large  boilers  the 
ratio  is  50  to  60  square  feet  of  heating  surface  per 
square  foot  of  grate.  • 

The  rate  of  combustion  for  anthracite  coal  will 
vary  from  2  to  6  pounds  of  coal  per  square  foot  of 
grate  surface  per  hour  with  average  draft.  With 
bituminous  coal  under  similar  circumstances,  3  to  8 
pounds  will  be  burned  in  the  smaller  boilers  and  8 
to  15  pounds  in  the  larger  sizes. 

The  air  opening  to  be  allowed  in  the  grates  depends 
upon  the  kind  of  coal,  but  usually  does  not  exceed  50 
per  cent  of  the  area  of  the  grate.  Anthracite  and  the 
better  grades  of  bituminous  coal  do  not  require  as 
large  opening  as  do  the  slack  coals. 

The  term  boiler  horsepower  as  applied  to  boilers 
has  no  definite  value  and  varies  with  local  customs, 
and  the  opinion  of  the  manufacturer. 

79 


Notes         on          Heating         and         Ventilation 

Boiler  Horsepower. — The  rating  of  a  boiler  should 
be  the  amount  of  steam  it  can  evaporate  with  good 
economy  and  without  producing  wet  steam.  In  pur- 
chasing a  boiler  specify  the  number  of  square  feet  of 
grate  surface  the  boiler  should  contain.  This  is  a 
better  criterion  of  the  work  that  the  boiler  will  do 
than  the  horsepower  rating.  The  American  Society 
of  Mechanical  Engineers  has  adopted  the  following 
rating  for  the  horsepower  of  a  boiler: 

A  boiler  horsepower  is  34^  pounds  of  water  evap- 
orated from  feed  water  at  212  degrees,  to  steam  at  212 
degrees,  which  is  called  the  from  and  at  evaporation. 
According  to  this  rule,  if  three  pounds  of  water  are 
evaporated  per  square  foot  of  heating  surface,  we  would 
allow  from  10  to  12  square  feet  of  heating  surface  for 
each  boiler  horsepower. 

The  American  Society  of  Heating  and  Ventilating 
Engineering  recommended  the  following  ratings  for 
cast-iron  house-heating  boilers : 

TABLE  XXVII. 

Rating    of    House-Heating    Boilers. 

Area  Coal  Burned  Total  Coal 

of  per  Hour  Burned  Rating  of 

Grate.  per  sq.  ft.  of  Grate.  per  Hour.  Boiler. 

Sq.  Ft.  Lbs.  Lbs. 

1  2.67  2.67  82 
1.5  2.96  4.44  140 

2  3.59  7.18  226 

3  4.21  12.63  390 

4  4.55  18.20  585 

5  4.88  24.40  780 

6  5.06  30.36  975 

7  5.24  36.68  1,165 

8  5.36  42.88  1,405 

9  5.48  49.32  1,650 

10  5.60  56.00  1,890 

11  5.71  62.81  2,125 

12  5.82  69.84  2,360 

13  5.93  77.09  2,595 

14  6.08  85.12  2,915 

15  6.23  93.45  3,235 

16  6.35  101.60  3,485 

17  6.46  109.82  3,730 

18  6.51  117.18  4,010 

19  6.55  124.45  4,285 

20  6.68  131.60  4,545 

21  6.61  138.81  4,800 

80 


Notes         on         Heating         and         Ventilation 

In  compiling  the  table  it  is  assumed — 

1.  That  the  area  of  the  grate  shall  be  the  area  of 
the  opening  in  which  the  grate  is  placed,  measured 
to  the  outermost  limits  of  air  openings. 

2.  That  the  boiler   is  to  be   used   under   average 
working  conditions,  carrying  steam  at  2  pounds  pres- 
sure;  that  the   draft  shall  be   sufficient   to   burn  the 
number  of  pounds  of  coal  per  hour  given  in  the  table, 
and  that  the   coal   used  shall   be   a  good   quality   of 
anthracite  coal  having  a  heating  power  of  13,000  B.  t.  u. 
per  pound  of  dry  coal. 

3.  That  the  rating  as  given  in  the  table  means  the 
number  of  square  feet  of  direct  radiation  steam  sur- 
face that  can  be  carried  by  the  boiler,  based  upon  the 
supposition  that  each  square  foot  of  direct  radiation 
steam  surface  emits  250  B.  t.  u.  per  hour  with  steam 
at  two  pounds  pressure  in  the  radiator  and  with  air 
surrounding  the  radiator  at  a  temperature  of  70  de- 
grees. 


CHAPTER  VI. 

STEAM  PIPING. 

In  designing  a  system  of  steam  piping  the  three  fol- 
lowing considerations  are  the  most  important :  First, 
that  the  piping  shall  be  so  arranged  that  all  condensed 
water  shall  drain  from  it;  second,  that  it  shall  be  free 
to  expand,  that  is,  so  arranged  that  the  joints  shall  not 
be  strained  when  the  piping  is  heated;  third,  that  all 
points  in  the  piping  at  which  air  would  accumulate  shall 
be  provided  with  some  means  of  removing  the  air. 

In  this  text  the  different  parts  of  the  piping  system 
referred  to  will  have  the  following  meaning : 

MAINS. — Mains  are  those  pipes  which  lead  from  the 
boiler  or  boiler  header  to  the  submains  or  risers.  Usu- 
ally there  are  no  radiators  tapped  from  these  mains. 

RISERS. — Risers  start  from  the  mains  in  the  base- 
ment or  attic,  and  extend  up  or  down  through  the  build- 
ing. From  the  risers  the  connections  to  the  individual 
radiators  are  taken. 

RETURNS. — All  piping  carrying  condensed  water  from 
the  steam  mains  to  the  boiler  is  included  in  the  return 
system.  The  terms  return  riser,  return  main,  etc.,  have 
the  same  significance  as  in  the  steam  system. 

RELIEFS  OR  DRIPS. — A  small  pipe  connecting  the 
steam  to  the  return  system  so  as  to  carry  condensed  wa- 
ter to  the  returns  is  called  a  relief  or  drip.  Drips  are 
used  at  all  points  where  water  would  collect  in  the  steam 
system.  These  drips  are  sometimes  made  of  large  pipe 
and  called  equalizing  pipes,  serving  to  equalize  the  pres- 
sure between  steam  and  return  mains  in  gravity  return 
systems. 

82 


Notes         on         Heating         and         Ventilation 

PITCH. — The  pitch  of  a  pipe  refers  to  its  inclination 
from  the  horizontal  pipe  lines.  It  is  best  that  pipes 
should  pitch  with  the  current  of  the  steam,  so  that  the 
steam  will  assist  in  the  removal  of  the  condensation. 
Return  pipes  are  usually  pitched  toward  the  boiler  so 
that  the  system  may  be  drained  at  that  point. 

WATER  LINE. — The  water  line  is  the  height  at  which 
the  water  stands  in  the  return  pipes.  In  a  well  designed 
gravity  system  it  is  seldom  more  than  twelve  inches 
above  the  water  line  of  the  boiler. 

SIPHON. — When  a  vertical  bend  is  made  in  the  return 
main  so  that  the  return  dips  down  and  returns  to  its 
former  level,  it  is  called  a  siphon.  All  siphons  should 
be  provided  with  a  drain  (or  pet  cock). 

DAMS. — Sometimes  the  water  level  in  the  boiler  is 
lower  than  that  desired  in  the  piping  system  and  an  in- 
verted siphon  is  placed  in  the  return  pipe.  No  return 
will  then  take  place  until  the  water  has  reached  the 
highest  point  of  this  bend  in  the  return.  A  dam  should 
be  provided  with  an  air  cock. 

WATER  SEAL. — Where  a  return  pipe  enters  the  return 
main  below  the  water  line  it  is  said  to  be  sealed.  It  is 
customary  to  seal  all  main  riser  drips  and  returns  from 
indirect  radiators  and  pipe  coils. 

WATER  HAMMER. — The  rattling  and  the  hammering 
often  heard  in  pipes  is  called  water  hammer.  It  is  caused 
by  steam  coming  in  contact  with  water  or  surface  in  the 
pipes  which  is  colder  than  itself.  A  sudden  condensa- 
tion results  and  a  vacuum  is  produced  into  which  the 
water  rushes.  The  blow  is  often  so -severe  as  to  crack 
the  fittings  and  spring  the  valves.  It  is  most  apt  to  oc- 
cur when  the  plant  is  first  started.  Accidents  from  this 
cause  may  be  avoided  by  admitting  the  steam  very  slow- 

83 


Notes 


o  n 


Heating         and 


Ventilation 


ly  at  first  and  draining  low  points  in  the  piping  system. 
STEAM  TRAPS. — Steam  traps  are  vessels  usually  placed 
between  the  steam  and  the  return  system  to  allow  the 
water  of  condensation  to  be  carried  to  the  return  sys- 
tem without  steam  entering  the  returns.  By  the  use  of 


Fij.    23. 

steam  traps  the  steam  and  return  mains  may  have  a 
wide  difference  of  pressure.  Steam  traps  are  objection- 
able as  they  are  liable  to  get  out  of  order  and  require 
frequent  repairs. 

Systems  of  Piping. — The    systems    of    piping    may 
be  grouped  under  three  general  heads.     First,  the  one- 

84 


Notes          on          Heating          and          Ventilation 

pipe  system.  In  this  system  the  pipe  carrying  the  steam 
to  the  radiator  also  returns  the  condensed  water  from 
the  radiator  to  the  boiler.  Second,  two-pipe  system,  in 
which  one  set  of  pipes  is  used  to  carry  the  steam  to 
the  radiator  and  an  entirely  separate  set  of  pipes  is  used 
to  carry  the  return  water  to  the  boiler.  Third,  a  com- 
bination of  these  two  systems.  The  usual  arrangement 
in  the  combination  system  is  to  run  the  mains  on  a  two- 
pipe  system,  but  the  connection  between  the  mains  and 
the  radiators  is  on  the  single  pipe  system.  The  one- 
pipe  system  has  certain  fundamental  advantages  over 
the  two-pipe  system.  In  the  one-pipe  system  the  steam 
and  condensed  water  are  always  at  the  same  temperature 
and  as  a  result  there  is  very  little  opportunity  for  water 
hammer.  In  the  two-pipe  system  the  steam  and  water 
being  separate  the  water  may  become  considerably  cooled 
below  the  temperature  of  the  steam,  and  if  at  any  point 
in' the  system  it  again  comes  in  contact  with  the  water 
we  have  condensation  of  the  steam,  vacuum  forms,  caus- 
ing water  hammer.  In  large  plants,  however,  the  one- 
pipe  system  is  not  desirable,  as  it  necessitates  carrying  a 
very  large  quantity  of  water  in  the  steam  mains. 

ONE-PIPE  SYSTEM. — The  simplest  of  all  piping  sys- 
tems used  in  steam  heating  is  what  is  known  as  the  one- 
pipe  gravity  system.  In  this  system,  the  steam  gener- 
ated in  the  boiler  flows  through  the  pipes  to  the  radia- 
tors where  it  is  condensed.  The  condensed  steam  in  the 
radiators  flows  back  through  the  same  piping  system  to 
the  boiler.  This  arrangement  necessitates  the  condensed 
steam  flowing  back  against  the  current  of  the  steam. 
This  is  objectionable,  as  there  is  a  tendency  to  trap  tlie 
water.  Because  of  this  tendency  it  is  good  practice  to 
make  the  pipes  larger  in  size  than  would  be  the  case 

85 


Notes         on         Heating         and         Ventilation 

if  the  steam  and  water  flowed  in  the  same  direction.  In 
the  one-pipe  gravity  system  the  pipe  should  always  be 
given  a  good  pitch  toward  the  boiler.  Figure  23  shows 
in  diagram  the  piping  and  radiator  connections  for  a 
one-pipe  system. 

Two-PiPE  SYSTEM. — In  the  two-pipe  system  one  sys- 
tem of  pipes  supplies  the  steam  and  another  system  car- 


Fig.  24. 

ries  off  the  water  of  condensation.  The  principal  object 
in  the  two-pipe  system  is  to  avoid  the  accumulation  of 
any  great  amount  of  water  in  the  radiators  or  mains 
and  in  that  way  give  a  more  positive  circulation.  Fig- 
ure 24  shows  the  general  arrangement  used  in  the  two- 

86 


Notes 


o  n 


Heating         and         Ventilation 


pipe    system.      The    indirect    radiators    and    pipe    coils 
should  always  be  connected  on  the  two-pipe  system. 

COMBINATION  SYSTEM. — In  ordinary  buildings  the 
most  satisfactory  method  is  to  use  a  combination  of  the 
one-pipe  and  the  two-pipe  systems.  In  this  system,  as 


Fig.  25. 

shown  in  diagram  in  Figure  25,  the  radiators 
and  risers  are  on  the  one-pipe  system,  while 
the  mains  are  installed  on  the  two-pipe  sys- 
tem. The  system  has  this,  advantage  over  the  one- 
pipe  system  of  mains,  that  the  mains  are  not  obliged 
to  carry  so  much  water  of  condensation  and  can  be  f  reec] 

•        87 


Notes 


o  n 


Heating         and         Ventilation 


from  water  from  time  to  time.  The  one-pipe  radiator 
connections  of  this  system  are  more  desirable  than  the 
two-pipe  radiator  connections  in  that  there  is  but  one 
valve  to  get  into  trouble  instead  of  two  and  the  steam 
and  the  water  of  condensation  are  always  in  contact  with 


03 


Fig.  26. 

each  other — thus  avoiding  the  danger  of  water  hammer. 
The  risers  may  be  one-pipe,  as  it  is  very  seldom  that  we 
have  difficulty  with  the  circulation  in  using  vertical  risers. 
In  most  cases  the  one-pipe  radiator  connections  and 
two-pipe  mains  will  be  found  to  give  the  best  satisfac^ 
tion. 


Notes          on          Heating          and          Ventilation 

OVERHEAD  DISTRIBUTION. — In  office  buildings  and 
buildings  where  the  basement  space  is  valuable  for  rental 
purposes,  it  is  desirable  to  place  the  steam  mains  where 
they  will  occupy  the  least  desirable  space.  It  is  custo- 
mary to  run  a  vertical  steam  main  to  the  attic.  A  set  of 
distributing  mains  is  run  through  the  attic,  from  which 


Fig.   27. 

vertical  risers  extend  down  through  the  building  with 
drip  pipes  connecting  to  the  return  system  at  their  low- 
er ends.  The  radiators  are  connected  to  the  risers  by 
means  of  single-pipe  radiator  connections.  This  system 
gives  very  satisfactory  results  as  in  all  cases  the  cur- 
rents of  steam  and  water  are  in  the  same  direction.  In 
buildings  exceeding  four  stories  in  height  it  is  usually 
necessary  to  provide  some  form  of  flexible  connection 


Notes         on         Heating         and         Ventilation 

to  allow  for  expansion.    A  system  of  this  kind  is  shown 
in  Figure  26. 

GRAVITY  SYSTEM. — Figures  23-26,  inclusive,  are  all 
shown  for  gravity  return  system  and  this  system  is  the 
one  commonly  used  for  all  small  buildings  and  for  resi- 
dences. In  this  system  the  steam  and  return  mains  are 
connected  to  the  boiler  without  the  introduction  of 
numps  or  traps,  so  that  the  condensed  steam  flows  back 
to  the  boiler  by  gravity.  Figure  27  gives  a  diagrammatic 
sketch  of  such  a  system.  If  the  pressure  at  the  surface 
of  the  water  in  the  boiler  is  the  same  as  the  pressure  of 
the  surface  of  the  water  in  the  return  mains,  then  the 
water  level  in  the  return  mains  and  in  the  boiler  will  be 
the  same.  But  if,  as  shown  in  Figure  27  by  the  dotted 
lines,  the  pressure  in  the  boiler  is  5  pounds  and  the  pres- 
sure is  only  4  pounds  when  it  gets  to  the  ends  of  the 
system,  then  the  system  is  no  loneer  balanced.  It  is  nec- 
essary for  the  water  to  rise  in  the  return  mains  until  the 
column  of  water  in  the  return  mains  is  of  sufficient 
height  so  that  its  weight  will  equal  a  pressure  of  1 
pound  per  square  inch,  or  approximately,  it  must  rise 
about  2.31  feet  so  that  the  water  in  the  return  main  will 
be  2.31  feet  higher  than  the  water  in  the  boiler,  and 
this  will  be  true  for  each  1  pound  difference  in  pressure 
between  the  steam  at  the  boiler  and  the  steam  at  the  ex- 
tremities of  the  system.  It  is  necessary,  then,  to  be  very 
careful  to  have  ample  sized  piping  in  this  system  so  that 
the  pressure  at  all  points  of  the  return  main  will  be  about 
equal.  In  addition,  it  is  necessary  that  the  steam  radia- 
tors, both  direct  and  indirect,  be  at  least  2  feet  above  the 
water  line.  For  the  reasons  given  above  it  is  not  desir- 
able to  operate  large  plants  on  the  gravity  return  sys- 
tem, as  this  system  requires  larger  expense  for  steam 

90 


Notes          on          Heating         and          Ventilation 

mains  and  more  or  less  difficulty  will  always  be  experi- 
enced in  starting  up  the  system.  The  systems  of  circu- 
lation involving  traps  and  pump  circulation  will  be 
taken  up  under  the  head  of  Central  Heating  Systems. 

Size  of  Steam  Return  Mains. — There  are  a  great 
many  rules  given  for  determining  the  size  of  steam  and 
return  mains,  all  of  which  must  be  more  or  less  modified 
to  meet  the  particular  case  in  hand.  In  fact,  a  very 
careful  determination  of  the  size  of  main  is  not  necessary, 
as,  no  matter  how  carefully  we  calculate  the  size  of  the 
main,  it  is  necessary  to  take  the  nearest  pipe  size.  In 
determining  the  size  of  the  main  two  conditions  must  be 
considered.  First,  it  must  be  of  sufficient  capacity  to  al- 
low of  free  circulation.  This  is  the  principal  considera- 
tion in  smaller  buildings.  Second,  the  mains  must  not 
produce  more  than  a  certain  drop  of  pressure.  This 
point  is  of  particular  importance  in  the  design  of  central 
heating  systems.  In  the  case  of  residences,  the  size  is 
determined  by  rules  determined  by  practice.  In  the 
second  place,  the  laws  governing  the  amount  of  pressure 
in  steam  pipes  are  fairly  well  known.  They  will  be 
treated  under  the  head  of  Central  Heating  Systems.  The 
most  rational  method  of  finding  the  size  of  mains  is  by 
determining  the  velocity  of  steam  passing  in  the  main. 
Knowing  the  weight  of  steam  passing  in  the  main  and 
having  the  pressure,  the  volume  of  steam  passed  through 
the  main  is  known.  This  volume  divided  by  the  allow- 
able velocity  in  feet  gives  the  area  of  the  pipe  in  square 
feet.  The  velocities  allowed  in  various  forms  of  mains 
are  as  follows: 

In  the  steam  engine  connections  from  75  to  100  feet 
per  second. 

In  exhaust  steam  mains  from  75  to  150  feet  per 
5econd. 

01 


Notes          on          Heating          and          Ventilation 

For  steam  heating  work  on  the  one  pipe  system,  pipes 
2  inches  and  under  10  feet  per  second. 

For  two-pipe  work,  pipes  2  inches  and  under  15  feet 
per  second. 

For  two-pipe  work,  pipes  2  to  4  inches  25  feet  per 
second. 

For  single-pipe  work,  low  pressure,  pipes  2  to  4 
inches  15  feet  per  second. 

For  single-pipe  work,  low  pressure,  pipes  4  inches 
and  over  30  feet  per  second. 

EXAMPLE. — Assume  that  a  main  is  to  supply  2,000  feet 
of  radiation.  This  radiation  gives  off  approximately 
1.70  B.  t.  u.  per  square  foot  of  radiating  surface  per 
degree  difference  of  temperature.  Let  the  tempera 
ture  of  the  steam  be  220°,  the  temperature  of  the 
room  70°.  Then  the  total  B.  t.  u.  transmitted  per 
hour  will  be  220—70X1.70X2,000=510,000.  At  220° 
the  latent  heat  of  steam  taken  from  the  steam  tables 
equals  966  B.  t  u.  Then  the  steam  used  per  hour 
will  be  510,000-f-966=527  pounds  of  steam.  At  220° 
each  pound  of  steam  has  a  volume  of  22.95  cubic  feet. 
Hence  we  have  527X22.95=12,000  cubic  feet  per  hour 
or  3.3  cubic  feet  per  second.  For  a  velocity  of  25 
feet  per  second  we  must  have  a  pipe  with  an  area  of 
.132  square  feet  or  19  square  inches.  This  is  approxi- 
mately the  area  of  a  5-inch  pipe. 

Miscellaneous  Rules  for  Size  of  Steam  Main.  RULE 
1. — The  following  is  a  very  common  rule  for  gravity 
return  systems:  To  determine  the  diameter  of  the 
main  leading  from  the  boiler,  point  off  two  places  in 
the  number  expressing  the  radiating  surface  and  take 
the  square  root  of  the  remainder.  To  apply  the  above 
rule  for  indirect  surfaces,  multiply  the  indirect  sur- 

99 


Notes 


o  n 


Heating         and         Ventilation 


face  by  seven-fifths  and  proceed  as  for  direct  sur- 
face. As  an  example,  suppose  we  are  to  supply  2,000 
square  feet  of  direct  radiation.  We  point  off  two 
places,  which  gives  us  20.  The  square  root  of  20  is 
4.48,  which  would  make  the  size  of  the  main  45^ 
inches. 

Table   XXVIII   gives   the   common   practice   in   pipe 


sizes: 

No.  of  Sq.  Ft. 
of  Radiation 

on  the 

Main  or  Riser. 
50    

100    

150    

200    

250    

300    

400    

500    

600    

800    

1,000    

1,500    

2,000    

3,000    

4,000    

6,000    


Steam 
Single 
Pipe 
System. 
IV2  inch 
2      inch 

2  inch 
2%  inch 
2Y2  inch 

3  inch 
3M>  inch 
3%  inch 
3%  inch 

4  inch 
4%  inch 
4%  inch 

5  inch 

6  inch 

7  inch 

8  inch 


TABLE  XXVIII. 


Steam  Main 

Steam  Riser      Steam  Riser 

Two  Pipe 
System. 

Single  Pipe            Two  Pipe 
System.                System. 

114  inch 
1%  inch 

1%  Inch 
1%  inch 

1^4  inch 
1%  inch 

1%  inch 

2      inch 

1%  inch 

2      Inch 

2%  inch 

2      inch 

2     inch 

2^z  inch 

2      inch 

2%  inch 

3     inch 

2%  inch 

3      inch 

3      inch 

2%  inch 

3     inch 

3      inch 

3      inch 

3%  inch 

3%  inch 

4     inch 

4      inch 

Very  liberal. 

4%  inch 

5      inch 

6      inch 

7      inch 

The  steam  supply  of  the  radiator  should  never  be 
less  than  1  inch.  Steam  mains  in  one-pipe  work 
should  not  be  less  than  \y2  inches  and  in  two-pipe 
work  less  than  1%  inches.  The  return  connections  to 
radiators  should  not  be  less  than  ^-inch  and  return 
mains  should  not  be  less  than  1  inch.  The  drip  pipe 
should  not  be  less  than  ^-inch.  Long  horizontal 
pipes  should  be  one-pipe  size  larger  than  the  verticals 
in  the  same  line.  In  the  overhead  system,  especially 
where  the  building  is  over  seven  or  eight  stories,  it 
is  well  to  make  the  risers  fairly  large  at  the  lower 
end  to  take  care  of  the  condensed  steam.  These  risers, 
even  at  the  lower  end,  should  not  be  less  than  \V2  inches 
in  size. 

9" 


Notes         on         Heating         and         Ventilation 


RETURN  MAINS. — Return  mains  cannot  be  figured  for 
returning  the  water  of  condensation  at  a  low  velocity 
alone,  but  allowance  must  be  made  for  the  very  sud- 
den demands  which  occur  when  the  plant  is  started 
and  for  the  air  carried  with  the  water.  The  size  of  the 
return  main  is  determined  almost  entirely  by  practical 
considerations. 

Table  XXIX  gives  the  relative  size  of  steam  and 
return  main  and  diameter  of  steam  main. 

Pipe  Drainage. — Return  mains  may  be  placed  on 
a  dead  level,  but  as  a  rule  it  is  desirable  to  give  them 
some  slight  pitch,  to  some  point,  preferably  the  boiler. 
At  its  lowest  point  there  will  be  provided  some  sort 
of  drain  cock  so  that  all  condensed  steam  may  be 
drained  out  of  the  system.  The  radiators,  as  well  as 

TABLE  XXIX.— RELATIVE  SIZE  OP  MAINS. 

Diameter  Diameter 

Steam  Pipe.  Return  Pipe. 

1%  1 

2  1 
2%  1% 

3  1% 

4  2 

5  2% 

6  3 
8  4 

10  4% 

12  5 

the  pipes,  should  be  set  so  that  the  condensed  steam 
may  drain  from  them  easily.  It  is  always  best  to 
drain  the  condensed  steam  with  the  steam,  in  which 
case  the  steam  tends  to  free  the  pipes  of  the  water 
of  condensation.  If  mains  are  long,  it  is  well  to  drain 
them  at  intervals  to  avoid  carrying  too  much  water 
of  condensation  with  the  steam.  In  the  gravity  return 
system  where  the  drip  pipes  connect  to  the  return  sys- 
tem, there  should  be  at  least  two  feet  difference  in 
level  between  the  steam  main  and  the  boiler  water 

94 


Notes 


on 


Heating         and         Ventilation 


level,  in  order  to  avoid  the  possibility  of  the  water 
from  the  boiler  being  forced  back  into  the  steam  main. 
Check  valves  will  not  prevent  it,  the  water  of  con- 
densation will  accumulate  in  the  return  main  above 
the  check.  If  it  is  necessary  to  drip  the  steam  main 
at  a  point  below  or  close  to  the  water  line,  then  it 


Fig.   28. 


should  be  drained  to  a  separate  system  of  piping  and 
the  condensed  steam  accumulating  in  this  piping 
should  be  forced  back  to  the  boiler  by  some  mechanical 
means.  Steam  connections  to  steam  mains  should  al- 
ways be  taken  from  the  top  of  the  mains  so  as  to  avoid 
the  draining  of  the  water  of  condensation  into  the  con- 

95 


Notes         on          Heating         and         Ventilation 

nections.  In  overhead  systems  of  piping  the  steam 
mains  may  be  drained  directly  through  the  risers  as  the 
amount  of  condensation  is  small  compared  to  the  num- 
ber of  drain  pipes.  In  this  case  the  risers  may  be  taken 
from  the  bottom  of  the  main.  In  connecting  radiators 
to  the  pipe  system  they  should  be  set  so  as  to  have  a 
slight  pitch  in  the  direction  in  which  they  are  intended 
to  drain.  Radiators  set  so  that  they  cannot  be  entirely 
drained  are  a  very  common  source  of  water  hammer. 

Expansion  of  Pipes. — The  expansion  of  pipes  in 
mains  exceeding  50  feet  in  length  becomes  an  impor- 
tant consideration.  It  is  customary  to  assume  that  in 
low-pressure  steam  piping  there  will  be  an  expansion  of 
1*4  inches  per  100  feet  of  pipe.  In  steam  mains  carry- 
ing a  pressure  of  80  pounds  or  over  it  is  customary  to 
allow  for  an  expansion  of  about  \y2  inches  per  100  feet 
of  length.  There  are  three  general  methods  of  taking 
up  expansion. 

First,  a  simple  means  is  by  making  offsets  and  turns 
in  the  pipe  every  100  to  200  feet,  the  expansion  being 
taken  up  by  the  spring  in  the  pipe.  This  is  shown  in 
Fig.  28.  This  method  is  seldom  used  except  in  pipes 
under  8  inches.  Another  method  and  the  method  which 
it  is  most  desirable  to  use,  is  to  take  up  the  expansion 
at  all  90°  turns.  In  this  method  the  pipe  when  it  reaches 
the  corner  turns  either  up  or  down  and  the  expansion 
is  taken  up  by  the  movement  around  the  vertical  nipple 
in  the  elbows  or  tees  at  the  corner.  This  method  of 
taking  up  expansion  is  shown  in  Fig.  29.  The  author 
has  had  the  opportunity  of  observing  a  system  installed, 
in  which  expansion  amounting  to  as  high  as  4  or  5 
inches  has  been  taken  up  in  swing  joints  of  this  kind 
and  the  joints  (which  have  been  in  use  for  over  twelve 
years)  have  given  no  trouble  whatever. 

96 


Notes          on          Heating          and          Ventilation 

The  third  method  is  by  use  of  expansion  joints.  The 
use  of  expansion  joints  is  in  general  not  to  be  recom- 
mended. Fig.  30  shows  a  cross-section  of  an  expansion 
joint.  Expansion  joints  are  quite  expensive  and  are  al- 
ways liable  to  leak  and  require  attention.  By  carefully 
laying  out  the  piping  most  systems  can  be  installed 
without  the  use  of  expansion  joints.  The  most  serious 
difficulty  occurs  in  the  modern  high  office  building.  In 


Fig.  29. 

buildings  of  not  over  ten  stories  expansion  joints  may 
be  avoided  by  anchoring  the  risers  in  the  middle  so 
that  they  expand  in  both  directions,  and  allowing  for  a 
flexible  connection*  between  the  risers  and  supply  main 
in  the  attic  and  return  main  in  the  basement.  In  this 
case  the  radiators  in  the  upper  and  lower  stories  of  the 
building  must  have  allowance  made  in  the  radiator  con- 
nections for  expansion  of  the  main. 

Another  method  that  has  been  used  to  allow  for  ex- 
pansion is  by  offsetting  the  pipe  at  about » the  middle 
story.  As,  for  example,  in  a  building  of  say  16  •  stories, 
run  the  riser  up  to  the  eighth  story,  tiien  offset  just  un- 
der the  ceiling  of  the  eighth  story  for  a  considerable 

97 


Notes         on         Heating         and         Ventilation 

distance,  usually  not  less  than  20  feet,  and  continuing 
the  riser  up  at  another  location.  The  principal  objec- 
tion to  this  method  is  its  appearance.  In  some  cases  it 
is  difficult  to  avoid  the  use  of  expansion  joints.  In 
using  expansion  joints,  the  joint  should  be  anchored  so 
that  the  expansion  will  go  in  a  definite  direction. 

Valves. — A  great  deal  of  consideration  should  be 
given  to  the  valving  of  a  steam  heating  system.  Gate 
valves  should  be  used  on  horizontal  steam  mains,  as  they 


Fig.   30. 

do  not  form  a  water  pocket.  If  globe  valves  are  used 
on  steam  mains,  they  should  be  placed  horizontally,  that 
is,  in  a  vertical  pipe  to  avoid  forming  a  steam  pocket. 
Where  it  is  possible  to  use  it,  an  angle  valve  makes  a 
very  desirable  form  of  valve.  In  large  buildings  where 
the  plant  will  be  under  the  control  of  an  engineer,  it  is 
desirable  to  place  valves  on  the  steam  risers  and  valves 
on  the  corresponding  return  risers.  In  residences  it  is 
well  to  avoid  valves,  particularly  on  return  mains.  A 
valve  on  the  return  main  is  particularly  dangerous,  as 
it  may  be  closed  by  accident  while  the  system  is  in  oper- 
ation, in  which  case  the  radiator  will  be  filled  with 
water  and  no  water  will  be  allowed  to  return  to  the 
boiler. 


Notes 


o  n 


Heating         and         Ventilation 


LOCATION  OF  MAINS  AND  RISERS. — Mains  and  risers 
should  be  located  in  as  inconspicuous  a  place  as  possible, 
at  the  same  time  they  should  be  accessible.  The  con- 
cealing of  mains  and  risers  in  the  building  construction 
is  always  a  questionable  practice.  If  it  is  necessary  to 
conceal  the  pipe  it  should  be  concealed  under  panels 
screwed  on  so  that  they  can  be  removed  in  case  of  leak- 
age or  other  necessary  repairs.  It  is  not  wise  to  at- 
tempt to  save  in  risers  by  making  long  radiator  con- 
nections. The  system  will  give  much  better  operation 


Fig.  31.     The  Simplest  Form  of  Connection.     Not  Desirable  if  Ex- 
pansion at   Right  Angle  is  Great. 

by  having  frequent  risers  with  shorter  radiator  con- 
nections. Where  risers  are  concealed  in  a  building  of 
wooden  construction  they  should  be  carefully  protected 
from  the  woodwork. 

CONNECTIONS   TO   MAINS  AND   TO   RISERS. 

In  making  the  connections  from  mains  to  risers  in  a 
steam  system  there  are  three  things  to  be  considered — 
the  drip,  the  expansion,  and  free  circulation.  The  sim- 

99 


Notes 


Heating          and          Ventilation 


plest  form  of  connection  in  shown  in  Fig.  31,  and  for 
general  purposes  it  is  perhaps  the  best  form  of  con- 
nection. The  expansion  of  the  main  in  the  direction 
of  its  length  is  taken  care  of  by  turning  in  the  threads 
of  the  vertical  pipes.  The  expansion  at  right  angles 
to  the  main,  which  is  ordinarily  very  small,  is  taken  care 
of  by  the  spring  of  the  pipes.  If  the  expansion  occurring 
at  right  angles  were  very  large,  then  some  other  form 
of  connection  would  be  desirable. 


f% 

i;?/fei 

11 


Fig.  32.     Using  a  45°    Ell   Instead  of  a  90°,   as  Shown   in  Fig.  31. 

Fig.  32  shows  a  similar  connection,  but  using  a  45- 
degree  elbow  in  space  of  a  90-degree  elbow  at  the  main, 
as  shown  in  Fig.  31.  This  connection  offers  less  resist- 
ance to  the  passage  of  steam  than  the  connection  shown 
in  Fig.  31 ;  oh  the  other  hand,  it  does  not  allow  of  as 
much  expansion.  The  pipe  rising  from  the  main  be- 
ing at  45  degrees,  there  is  a  limited  opportunity  for  any 
turning  in  the  threads  of  the  pipe  and  expansion  is  taken 
up  by  the  spring  of  the  pipe.  In  this  figure  a  drip  is 
shown  at  the  bottom  of  the  riser.  A  drip  is  often  placed 
at  this  point,  particularly  in  large  buildings.  In  smaller 

100 


Notes 


o  n 


Heating         and         Ventilation 


plants  condensation  is  carried  back  through  the  steam 
connection  itself,  as  in  Fig.  31.  In  larger  buildings  it  is 
undesirable  to  carry  so  much  condensation  through  the 
horizontal  pipes  and  a  drip  is  placed  at  the  bottom  of 
the  riser,  as  shown  in  Fig.  32. 

Fig.  33  shows  a  connection  similar  to  that  in  Fig.  31. 
It  allows  free  expansion  of  the  main,  the  same  as  Fig. 
31.  In  Fig.  33  all  the  condensation  which  has  occurred 


Fig.    33.      Allows   for    Expansion    of   the    Main;    Requires    a    Drip    at 
the    Point   where    Riser    Starts. 

in  the  main  up  to  this  connection  will  drain  into  the 
connection  and  it  is  therefore  necessary  to  place  a  drip 
at  the  point  where  the  riser  starts.  A  connection  of  this 
kind  is  often  used  where  it  is  desired  to  meter  different 
riser  connections  for  different  consumers,  then  the  con- 
densation for  each  riser  or  each  set  of  risers  can  be  col- 
lected and  metered  with  very  little  possibility  of  its  com- 
ing back  into  the  main.  This  is,  in  some  respects,  an 
undesirable  form  of  connection.  If  for  any  reason  the 
water  level  rises  in  the  return  system  above  the  hori- 
zontal pipe  connection  to  the  riser,  then  the  riser  will  be 

101 


Notes         on         Heating         and         Ventilation 


entirely  sealed  from  the  main  and  it  will  be  impossible 
to  get  steam  into  the  riser.  The  writer  has  experienced 
this  difficulty  in  places  where  it  was  necessary  to  use  this 


Fig.   34.      Often    Used    in    Limited    Headroom.      Usually    Undesirable. 


Fig.   35.      A    Different  Way  of   Carrying   Off  the   Drip;   Used   Where 
Drip  is  Taken  Off  at  End  of  Main. 

form  of  connection.     This  happens  particularly  in  grav- 
ity return  systems. 

Fig.  34  shows  a  form  of  connection  often  used  where 

102 


Notes         on         Heating         and         Ventilation 

there  is  very  limited  head  room.  As  a  general  rule  this 
form  of  connection  is  a  very  undesirable  one.  It  allows 
almost  no  expansion,  all  expansion  in  such  a  connection 
must  be  taken  up  in  the  spring  of  the  pipes.  In  addition 
to  this,  if  the  main  happens  to  carry  a  large  amount  of 
water  of  condensation,  part  of  this  condensation  may 
flow  into  the  horizontal  pipe  and  impede  the  circulation 
in  the  horizontal.  Under  the  same  conditions  if  a  con- 
nection such  as  is  shown  in  Fig.  31  or  Fig.  32  were  used, 
no  difficulty  would  be  experienced. 

Fig.  35  shows  another  method  of  carrying  off  the 
drip.  This  arrangement  is  used  where  the  drip  is  to  be 
taken  away  at  the  end  of  the  main.  It  is  very  often 
desirable  at  such  points,  particularly  if  the  main  is  long, 
to  remove  the  air  from  the  pipe.  The  figure  shows  an 
air  valve  placed  at  the  end  of  the  pipe.  Locating  an 
air  valve  at  the  end  of  a  main  near  the  point  of 
the  drip  facilitates  the  rapidity  of  the  circulation  in  the 
main.  In  a  great  many  installations  all  the  air  in  the 
system  is  taken  care  by  means  of  the  radiator  air  valves. 
Such  an  arrangement,  particularly  if  the  house  be  large, 
always  makes  the  system  slow  in  circulation.  In  the 
larger  systems  it  is  absolutely  imperative  that  the  steam 
mains  be  properly  relieved  of  air.  In  addition  to.making 
the  steam  slow  in  circulation,  it  causes  unequal  expansion 
of  the  piping.  This  trouble  will  be  taken  up  in  another 
chapter. 

Fig.  36  shows  the  connection  of  the  drips  from  two 
mains  to  a  single  drip  pipe.  Such  an  arrangement,  while 
simple,  is  undesirable,  as  the  condensation  from  one  main 
often  interferes  with  the  condensation  coming  from  the 
other  main.  This  would  give  very  little  trouble  if  the 
connection  were  made  above  the  water  line.  The  ob- 

103 


Notes         on         Heating         and         Ventilation 

j  action,  however,  to  making  such  connection  above  the 
water  line  is  that  if  the  two  currents  of  condensation 
which  meet  at  this  point  are  not  at  the  same  tempera- 
ture, hammering  or  a  chattering  noise  results.  If  placed 


Fig.  36.     Drips  from  Two  Mains  to  a  Single  Drip  Pipe.     Simple  but 
Undesirable. 

below   the    line    there    is    an    opportunity    for   the   two 
streams  of  water  to  interfere  with  the  circulation. 

A  better  arrangement  is  that  shown  in  Fig.  37,  in 
which  the  two  streams  of  water  coming  as  drip  from 
the  steam  mains  would  not  strike  each  other  in  the  same 


104 


Notes          on          Heating         and          Ventilation 

line;  the  one  stream  would  flow  into  the  other.  The 
union  of  the  two  streams  should  occur  below  the  water 
line  of  the  system,  if  possible. 

Fig.   38   shows   a  connection   from  main  to   riser,   in 


Fig.   37.      A    Better  Arrangement   of   Dripping   Two   Mains   into   One 
Drip    Pipe. 

which  the  head  room  is  very  short  and  it  is  desired  to 
take  up  a  large  amount  of  expansion,  the  expansion  be- 
ing taken  /up  by  a  swing  on  the  short  vertical  nipple  and 
by  a  swing  on  the  riser..  This  connection  has  been  used 

105 


Notes 


on 


Heating         and         Ventilation 


for  tunnel  mains  where  the  head  room  in  the  tunnel  did 
not  permit  of  the  other  forms  of  connection  shown. 

Fig.  39   shows  the  connection  between  the  main  and 
the  riser  in  an  overhead  system  of  distribution  in  which 


38. 


Connection  from    Main  to   Riser  Where   Headroom   is   Very 
Short    and    Expansion    Great. 


the  rooms  in  the  upper  story  are  used  and  it  is  desired 
to  conceal  the  piping  connections. 

As  shown  in  Fig.  39,  the  connection  from  the  main 
to  the  riser  is  carried  in  the  space  between  the  roof  and 
the  ceiling  of  the  room  below.  The  connection  from  the 
main  to  the  riser  is  taken  from  the  bottom  of  the  main. 
This  is  not  objectionable  in  an  overhead  system,  as  each 

106 


Notes 


on 


Heating         and         Ventilation 


riser  has  a  drip  at  the  bottom  and  becomes  in  itself  a 
drip  main,  and  in  some  cases  this  is  the  desirable  thing 
to-do,  as  it  keeps  the  steam  and  main  entirely  relieved  of 
condensation  at  all  points. 


Fig.    39. 


Connection    from    Main    to    Riser    in    Overhead    System    of 
Steam   Distribution. 


In  making  connections  between  mains  and  risers  an 
endeavor  should  be  made  to  locate  the  main  so  that 
the  horizontal  pipe  connecting  main  to  the  riser  will  not 
be  too  long,  just  enough  to  allow  for  expansion.  If  it 

107 


Notes 


Heating          and          Ventilation 


is  necessary  to  make  this  a  long  pipe,  then  the  pipe 
should  be  made  one  pipe  size  larger  than  would  other- 
wise be  used,  particularly  in  the  single  pipe  system.  In 
the  double  pipe  system  long  horizontals  are  not  so  ob- 


Fig.    40.    Simplest   Form;  Short;   Drains  Easily,  but   Does   Not  Allow 
for  Expansion  of  Riser. 

jectionable,  as  the  riser  may  be  dripped  at  its  lower  end, 
as  shown  in  Fig.  32. 

In   residence   work   it   is   usually   found   desirable   to 
connect  directly  from  the  steam  main  to  the  radiators 

108 


Notes         on          Heating 


and 


Ventilation 


on  the  first  floor  instead  of  connecting  these  radiators 
to  the  risers.  This  direct  connection  from  the  radiator 
to  the  main  insures  a  quicker  circulation  of  the  first 
floor  radiators,  which  is  usually  found  desirable  in  resi- 
dence work.  In  building  work  this  is  not  usually  the 


Fig.  41. 


Horizontal    Connection    Long    Enough    to    Care   for   Some 
Expansion   of   Riser   by  the   Spring   of  the   Pipe. 


case,  the  first  floor  radiators  are  connected  to  the  main 
risers. 

Radiator  Connections. — The  connection  between 
the  radiators  and  the  risers  should  always  be  carefully 
considered.  There  are  a  great  many  forms  of  connec- 
tion used  between  the  radiator  and  the  riser  to  which  it 

109 


Notes 


o  n 


Heating         and         Ventilation 


is  connected.  Each  of  these  different  forms  of  connec- 
tion has  its  advantage  and  disadvantage,  which  must  be 
considered  in  using  any  particular  type  of  connection. 
Figures  40  to  46  deal  with  single  pipe  work. 

Fig.  40  is  the  simplest  form  of  connection.    Its  advan- 
tage is  that  it  is  short,  simple  and  drains  easily.     The 


Fig.    42. 


Desirable,    Clean,    but    Floor    Must    Come    Up    When    the 
Trouble-Man    Comes. 


disadvantage  of  this  form  of  connection  is  that  it  does 
not  allow  of  any  expansion. 

The  expansion  of  the  riser  would  lift  one  end  of  the 
radiator  off  the  floor  and  in  all  probability  produce  a 
leaky  joint. 

Fig.  41  is  a  similar  form  of  connection,  but  the  con- 
nection between  the  valve  and  the  riser  is  long  enough 
so  that  a  certain  amount  of  expansion  can  be  taken  care 

110 


Notes 


o  n 


Heating         and         Ventilation 


of  by  the  spring  of  the  pipe  which  connects  the  radiator 
valve  and  the  riser. 

Fig.  42  is  a  very  common  form  of  connection  used 
in  residence  work.  The  advantage  of  this  connection 
over  the  connections  shown  in  Figs.  40  and  41  is  that 
where  the  pipe  passes  over  the  floor  there  is  always 
opportunity  for  dirt  to  collect  around  and  under  the  pipe 
and  it  is  difficult  to  sweep  this  dirt  out.  The  connection 
shown  places  the  horizontal  pipe  in  the  joist  space* 


Fig.  43.     Similar  to  Fig.  3,  with   Position  of  Radiator  Changed. 

The  long  horizontal  pipe  under  the  floor  allows  a  cer- 
tain amount  of  expansion  due  to  the  spring  of  the  pipe. 
On  the  whole  this  is  a  desirable  form  of  connection.  Its 
principal  objection  is  that  it  cannot  be  easily  reached  in 
case  of  accident  and  it  cuts  the  joists.  The  most  com- 
mon trouble  with  such  connection  is  to  have  a  sand 
hole  in  the  elbow.  Of  course  to  repair  this  it  would  be 
necessary  to  take  up  the  floor. 

ill 


Notes          on          Heating          and          Ventilation 

Fig.  43  is  practically  the  same  as  Fig.  42,  the  position 
of. the  radiator  being  changed. 

Fig.  44  shows  the  arrangement  of  radiator  connection 
in  which  the  horizontal  is  dropped  down  under  the  ceil- 


Fig.   44.      Sometimes    Used    on    Upper    Floors,    Horizontal   Pipe   Ex- 
posed   Below   Ceilings    Is   An    Objection.      Will    Do  for  Store 
Undecorated    Rooms. 

ing  of  the  room  below.  This  connection  is  sometimes 
used  on  upper  floors.  The  objection  to  it,  however,  is 
that  the  horizontal  pipe  coming  just  below  the  ceiling  is 
very  unsightly,  and  it  should  be  used  only  where  the 

112 


Notes         on         Heating         and         Ventilation 


Fig.  45.     Used   in  Office   Buildings;  Good   Form  for  Fireproof 
Buildings. 


Fig.   46.      Commonly   used    in    Residence   Work,   Where   First    Floor 
Radiators  are   Fed  from    Main   lit  Cellar. 

113 


Notes         on         Heating         and-     Ventilation 

horizontal  pipe  is  exposed  in  store-rooms  or  through  un- 
decorated  rooms  where  such  pipe  would  not  be  objec- 
tionable.' 

Fig.  45  is  the  plan  of  a  connection  very  commonly 
used  in  office  buildings.  The  connection  is  made  from 
the  riser  to  the  radiator,  passing  the  pipe  behind  the 
radiator  and  using  a  corner  valve  where  the  radiator 


Fig.  47.     The  Simplest  Connection  for  a  Two-Pipe  System. 

connection  attaches  to  the  main.  The  principal  ob- 
jection to  this  arrangement  is  that  it  throws  the  radiator 
out  some  distance  into  the  room  and  it  is  very  difficult 
to  sweep  around  the  connection  so  as  to  keep  it  clean. 
In  buildings  of  fireproof  construction  and  where  a  large 
amount  of  expansion  is  to  be  taken  care  of,  this  is  prob- 
ably the  best  form  of  connection  to  use. 

114 


Notes 


o  n 


Heating         and         Ventilation 


Fig.  46  shows  a  connection  similar  to  Fig.  44  for  first 
floor  radiators.  It  is  customary  in  most  buildings  to  con- 
nect the  first  floor  radiator  directly  to  the  main  and  not 
to  a  riser.  This  arrangement  is  commonly  used  in  resi- 


in  Buildings  Not  More  Than    Three   Stories   in    Height. 
Fig.  48.     Expansion  Taken  Up  by  Spring  in  Horizontal  Pipes. 


Used 


dences.  The  connection  is  such  that  we  have  very  easy 
turns  and  a  very  slight  resistance  for  the  passage  of 
condensation. 

115 


Notes          on          Heating         and         Ventilation 


msmm 


Fi3.  49.     Radiator  on   First   Floor  and   Horizontals  in   Basement. 

116 


Notes          on          Heating          and          Ventilation 

Fig.  47  shows  the  simplest  form  of  radiator  connec- 
tion for  the  two-pipe  system.  The  objection  to  this  ar- 
rangement is  similar  to  the  objection  made  to  Fig.  40. 
That  is,  it  is  very  rigid  and  will  permit  of  almost  no 
expansion  and  should  only  be  used  where  the  radiator 
is  located  at  such  a  point  that  it  is  not  necessary  to  take 
up  expansion.  The  connection  is  simple  and  direct, 
and  from  the  standpoint  of  circulation,  a  desirable  one. 

Fig.  48  shows  a  connection  in  which  the  expansion  is 
taken  up  by  means  of  the  spring  in  the  horizontal  pipes. 
The  verticals  to  the  radiator  valves  may  be  made  shorter 
and  these  connections  can  all  be  concealed  in  the  joist 
space  if  desired.  This  arrangement  can  be  used  for 
buildings  not  more  than  three  stories  in  height.  Where 
buildings  are  higher  the  two-pipe  connection  should  be 
made  with  a  series  of  elbows,  allowing  for  free  expan- 
sion— something  like  that  shown  in  Fig.  45. 

Fig.  49  shows  a  two-pipe  radiator  connection  where 
the  radiator  is  on  the  first  floor  and  the  horizontals  are 
located  in  the  basement.  The  same  connection  is  shown 
with  a  horizontal  pipe,  allowing  for  expansion.  In  this 
case  the  return  connection  is  shown  entering  directly 
into  the  return  main  without  any  elbow.  This  is  always 
undesirable,  as  the  connection  is  very  rigid,  not  allow- 
ing for  expansion,  and  should  only  be  used  where  the 
connection  will  not  be  affected  by  expansion.  If  expan- 
sion must  be  allowed  for  in  the  return  main  then  a  con- 
nection similar  to  that  shown  for  the  steam  main  should 
be  used. 

Fig.  50  shows  the  radiator  connection  for  automatic 
system  of  heat  control  on  the  double-pipe  svstem.  In 
this  case  it  is  quite  common  to  put  the  automatic  valve  on 
the  steam  supply  and  the  check  valve  on  the  return. 

117 


Notes         on          Heating         and         Ventilation 


Then  when  the  steam  is  turned  off  by  the  thermostat, 
the  check  valve  automatically  closes,  and  there  is  no 
possibility  of  the  steam  or  water  in  the  return  main 


Fig.  50. 


Connection  for  Automatic  System  of  Heat  Control  on  the 
Double- Pipe   System. 


getting  back  into  the  radiator.  If  no  check  were  placed 
upon  the  return  a  vacuum  would  be  formed  in  the  ra- 
diator, due  to  the  condensation,  and  the  water  would  be 


.  i  • 
118 


Notes         on         Heating         and         Ventilation 

drawn  back  from  the  return  main  into  the  radiator  by 
this  vacuum;  then  when  the  steam  was  again  turned  on 
this  water  would  cause  a  severe  hammer  in  the  radia- 
tor. A  still  better  arrangement  is  to  put  an  automatic 
valve  on  .both  supply  and  return. 

In  planning  radiator  connections  for  a  building  a  long 
horizontal  should  be  avoided,  the  length  should  be  only 
sufficient  to  take  up  expansion. 

The  location  of  the  radiator  should  be  carefully  se- 
lected, so  as  not  to  occupy  the  best  space^in  the  room. 
For  example,  it  is  not  uncommon  to  find  the  radiator 
in  a  bedroom  occupying  the  only  place  in  the  room  for 
the  bed.  The  position  of  the  radiators  should  be  select- 
ed also  with  reference  to  the  risers,  so  as  to  make  the 
connections  as  short  and  direct  as  possible.  The  form 
of  connection  should  be  such  as  to  allow  for  proper  ex- 
pansion. 

SUPPORTING  OF  PIPES. — Horizontal  pipes  are  usually 
supported  by  the  ordinary  form  of  expansion  hanger. 
As  a  rule  pipes  should  be  supported  every  10  feet  and 
should  be  supported  at  points  bearing  the  greatest  weight. 
Tn  placing  a  pipe  support  care  should  be  taken  to  see 
that  each  support  bears  its  proper  proportion  of  weight. 
Tn  buildings  over  three  stories  in  height  means  should 
be  taken  to  carry  the  weight  of  the  risers.  An  iron 
strap  passing  around  the  pipe  and  bolted  to  some 
portion  of  the  building  structure  is  usually  the  best 
means.  Large  piping  is  often  supported  by  chains  or  on 
brackets  with  rollers.  The  supports  of  large  pipes  will 
be  taken  up  under  the  subject  of  Central  Heating. 


119 


CHAPTER  VII. 

DESIGN  OF  A  HOT  WATER  HEATING 
SYSTEM. 

Hot  water  heating  plants  may  be  divided  into  two 
classes,  those  using-  natural  circulation,  and  those  using 
forced  circulation.  In  residences  and  small  buildings  the 
system  using  natural  circulation  is  almost  universally 
used.  It  is  simpler  in  construction  and  cheaper  to  in- 
stall and  operate.  In  central  hot  water  heating  systems 
and  in  the  larger  buildings  the  forced  system  of  circula- 
tion is  employed.  It  is  more  certain  in  circulation,  the 
size  of  the  pipes  may  be  smaller  and  in  such  buildings 
the  system  mav  be  cared  for  by  an  expert  attendant. 
The  systems  of  forced  circulation  will  be  discussed  in 
connection  with  central  heating. 

Natural  System. — The  arrangement  of  the  hot  wa- 
ter boiler  and  of  the  piping  in  a  hot  water  heating 
plant  is  similar  to  that  of  a  two-pipe  steam  system,  the 
difference  is  only  in  minor  changes  in  the  piping  system. 
The  circulation  in  a  natural  hot  water  heating  system  is 
produced  bv  the  difference  in  the  weight  of  the  water  in 
the  cold  and  the  hot  leg  of  the  system.  It  depends  verv 
largely  upon  the  height  of  the  water  column  in  the  cold 
les*.  The  difference  in  the  weight  of  the  water  in  the 
two  legs  of  the  system  is  due  to  the  fact  that  water 
weiehs  less  per  cubic  foot  as  its  temperature  is  in- 
creased, namely: 

At  130°  the  weight  of  water  per  cubic  foot  is  61.56 
pounds.  At  140°  the  weight  of  water  per  cubic  foot  is 
61.37  pounds.  If,  then,  there  were  one  cubic  foot  of* 

180 


Notes          on          Heating         and         Ventilation 

water  in  both  hot  and  cold  legs  of  the  system  with  a  dif- 
ference of  10°  between  the  two  sides,  the  force  to  pro- 
duce circulation  would  be  .19  pound.  It  will  be  seen 
from  this  that  the  force  going  to  produce  circulation  is  a 
small  one  and  may  be  easily  overcome  by  the  resistance 
of  the  piping  system.  It  is  important,  then,  that  in  in- 
stalling a  hot  water  system  considerable  attention  be 
given  to  the  arrangement  of  the  piping. 

Loss  of  Heat  from  Radiators. — In  designing  a  hot 
water  system  the  losses  of  heat  from  the  building  would 
be  computed  by  the  same  rules  as  previously  given  for 
other  systems.  These  losses  of  heat  having  been  deter- 
mined, it  will  be  necessary  to  replace  the  loss  by  the 
heat  given  off  by  the  radiator.  In  order  to  determine 
the  amount  of  radiation  necessary  we  must  know  what 
the  losses  of  heat  per  square  foot  are  for  hot  water 
radiators.  Table  30  gives  the  results  obtained  from  hot 
water  radiators  tested  under  actual  operating  conditions 
with  hot  water.* 

Table  XXX  shows  that  the  rate  of  transmission,  as 
given  in  the  last  column  of  the  table,  is  almost  the  same 
as  for  steam  radiators.  It  will  be  safe  to  assume  that 
TABLE  xxx. 


I             !     !     i  ?l 

<M                                   B             £              "S  §,£ 

0                                                          .  C  £  C      .3 

•CJ                                                           ft                     ft                       ft  '"-MK« 

e                           s          s           s  Sd-  ?r8 

5  EHEH£3W3£'° 

38"  3-column   cast  iron.. 187             182                 72  180  -  Cfl 

38"  2-column   cast   iron..  190             185                 70  200  170 

38"  flue  radiator   182.5         178.5             70  181  165 

38"  2-column   cast  Iron.. 172.5         167.5             70  150  1.'50 

the  hot  water  radiator  would  give  off  the  same  amount 
of  heat  per  square  foot  whether  filled  with  steam  or  hot 

121 


Notes         on          Heating         and         Ventilation 

water,  the  temperature  inside  and  outside  of  the  radiator 
being  the  same.  This,  however,  is  not  the  case,  as  it  is 
customary  to  operate  a  hot  water  plant  at  a  temperature 
not  exceeding  180°  or  less.  In  calculating  heating  sur- 
faces, the  temperature  of  the  water  should  never  be  as- 
sumed higher  than  170°.  The  temperature  being  about 
220°  under  ordinary  conditions  in  a  steam  radiator  and 
only  170°  in  the  hot  water  radiator,  the  total  transmis- 
sion in  the  hot  water  radiator  is  only  about  65  per  cent 
of  the  transmission  by  the  steam  radiator  using  steam. 

There  is  another  consideration  in  hot  water  heating. 
The  lower  the  temperature  of  the  radiating  surface  the 
more  uniform  the  temperature  of  the  room  and  the  more 
agreeable  the  heating  effect.  Where  it  is  desired  to  heat 
almost  uniformly  all  portions  of  a  room,  regardless  of 
initial  expense,  it  may  be  accomplished  by  installing  very 
large  heating  surfaces.  The  reason  for  this  is  easily 
explained.  Where  the  radiating  surfaces  are  kept  at  a 
high  temperature,  say  200°  or  over,  at  least  50  per  cent 
of  the  heat  is  given  off  by  radiation  and  the  remaining 
heat  is  given  off  by  contact  of  air.  When  the  tempera- 
ture of  the  radiating  surface  is  lowered  a  large  propor- 
tion of  heat  is  given  off  by  contact  of  air  and  a  smaller 
portion  by  radiation.  This  allows  the  air  in  the  room  to 
be  at  nearly  the  same  temperature  as  the  objects  in  the 
room.  It  is  possible,  then,  in  a  hot  water  system  to  use 
quite  different  amounts  of  radiation,  depending  upon  the 
effect  desired.  This  may  be  illustrated  by  an  example. 

INDIRECT  HOT  WATER  RADIATORS. 
Suppose    a    room    to   lose    10,000    B.  t.  u.  per   hour 
and    that   the    heating   surface   has   the    same    rate   of 
transmission  whether  steam  or  water  is  used,  and  that 

18* 


Notes         on          Heating         and         Ventilation 

this  rate  of  transmission  be  1.5  B.  t.  u.  per  square  foot 
per  degree  difference  of  temperature.  In  the  first 
case,  let  the  room  be  heated  by  steam.  The  tempera- 
.ture  of  steam  in  the  radiator  be  220°  and  the  tempera- 
ture of  the  room  70°.  Then  the  heat  loss  per  square 
foot  of  surface  would  be  (220—70)  X  the  rate  of  trans- 
mission, 1.5  =  250  B.  t.  u.  The  number  of  feet  of  radia- 
tion required  to  heat  the  room  will  be  10,000-^-250=40 
sq.  feet. 

In  the  second  case,  suppose  the  room  to  be  heated  by 
hot  water  radiator  at  a  temperature  of  170°.  Then  the 
B.  t.  u.  given  off  per  square  foot  of  surface  would  be 
(170— 70)X1.50=150.  The  number  of  square  feet  of 
radiation  required  to  heat  the  room  would  be  10,000-=- 
150—66  square  feet. 

In  the  third  case,  assume  a  residence  in  which  a  very 
uniform  heating  condition  is  desired  and  the  tempera- 
ture of  the  heating  surface  is  not  to  exceed  150°.  The 
loss  per  square  foot  of  radiation  would  be  (150 — 70  )X 
1.50=120  B.  t.  u.  The  radiation  required  would  then  be 
10,000-^120=83  square  feet.  The  amount  of  radiation 
in  hot  water  heating  depends,  then,  upon  the  effect  de- 
sired. 

In  a  closed  tank  system  it  would  be  entirely  possible 
to  obtain  a  temperature  as  high  as  240°  or  250°.  In  the 
open  tank  system  the  temperature  should  never  exceed 
180°,  as  a  higher  temperature  than  this  would  form 
steam  in  the  tank  and  there  would  be  danger  of  the  wa- 
ter boiling,  which  causes  a  cracking,  hammering  sound 
in  the  piping  system. 


123 


Notes         on          Heating         and         Ventilation 

TABLE  XXXI.— INDIRECT  HOT  WATER  RADIATORS. 

The  following  table  gives  the  emission  of  heat  by  indirect  hot 
water  radiators  per  square  foot  per  hour  per  degree  difference  in 
temperature: 

Velocity  of  Air  in  Feet  British  Thermal 

Per  Minute.  Units. 

174  1.70 

246  2.00 

300  2.22 

342  2.38 

378  2.52 

400  2.60 

428  2.67 

450  2.72 

474  2.76 

492  2.80 

The  difference  between  170  degrees  (average  tem- 
perature of  the  water  in  the  radiator)  and  55  degrees 
(average  temperature  of  the  air  passing  through  the 
radiator)  being  115,  the  efficiency  at  240  feet  velocity 
per  minute  is  2.  B.  t.  u.  per  degree  difference  or  230 
B.  t.  u. 

Ordinarily  the  amount  of  indirect  radiation  required  is 
computed  by  adding  a  percentage  to  the  amount  of  di- 
rect radiation,  and  an  addition  of  50  per  cent  has  been 
found  sufficient  in  many  cases.  When  accurate  results 
are  required  it  is  better  to  figure  the  heat  loss  as  given 
in  Table  XXXI. 

Free  area  between  the  sections  of  radiation  to  allow 
passage  of  the  required  volume  of  air  at  the  assumed 
velocity  must  be  carefully  maintained.  The  cold-air 
supply  duct,  on  account  of  less  frictional  resistance, 
may  ordinarily  have  80  per  cent  of  the  area  between  the 
radiator  sections.  The  hot  air  flues  may  safely  be  pro- 
portioned for  the  following  air  velocities  per  minute : 
First  floor,  200  feet ;  second  floor,  300  feet ;  third  floor, 
400  feet. 

Rules  for  Hot  Water  Heating.— Rule  1.— Divide 
the  volume  of  the  room  by  55.  Add  %  of  the  exposed 

124 


Notes 


o  n 


Heating         and         Ventilation 


wall  surface.  Add  the  glass  surface.  Multiply  the  sum 
of  these  by  .4,  the  product  will  be  the  square  feet  of 
direct  hot  water  radiation  required. 

Rule  2. — For  ordinary  rooms  divide  the  exterior  wall 
surface  by  4;  add  the  glass  surface  and  multiply  the 
sum  by  .55.  For  entrance  halls  multiply  the  sum  by  .7. 

Rule  3. — Divide  the  volume  of  the  room  in  cubic  feet 
by  the  factors  given  below  and  the  quotient  will  be  the 
radiating  surface  in  square  feet. 

First  floor  rooms,  1  side  exposed 40 

First  floor  rooms,  2  sides  exposed 37 

First  floor  rooms,  3  sides  exposed .34 

Second  floor  rooms 45 — 50 

Halls  and  bath  rooms 35 

Offices    37—50 

In  all  these  rules  factors  of  exposure  are  to  be  allowed 
as  given  on  pages  21  to  27. 

In  order  to  understand  better  the  methods  of  deter- 
mining the  heating  surface  required  for  a  given  house, 
take  the  same  house  as  figured  for  steam  on  page  77. 

TABLE   XXXII.— RESULTS   OF  COMPUTATIONS— DIRECT  HOT 
WATER. 

B.    t.    u. 

from 
Table  XII. 

First  Floor — 

Parlor    10,395 

Sitting  room 7,035 

Dining  room 7,350 

"Kitchen    10,300 

Hall    7,035 

Second  Floor — 

W.   chamber 10,050 

Alcove   7,560 

S.    chamber 7,035 

N.   chamber 7,455 

Bath 3,150 

E.   chamber 5,250 

Halls    2,730 

*Just  enough  radiation  to  keep  from  freezing  in  extremely  cold 
weather. 

125 


Radiating 

Radiating 

Surface, 

Radiating 

Surface 

2-Column 

Surface 

Actually 

Cast  Iron. 

Rule  3. 

Installed. 

68 

45 

C8 

46 

52.5 

50 

48 

48 

48 

67.5 

47 

40 

46 

32.5 

48 

65 

39 

65 

49 

18 

40 

46 

34.5 

46 

49 

32 

50 

20 

12 

20 

34 

25 

34 

18 

25 

20 

Notes         on         Heating         and         Ventilation 

In  Table  XXXII  the  second  column  gives  the  B.  t. 
u.,  as  determined  in  Table  XXI,  column  3.  Column 
3  gives  the  radiation  in  square  feet  for  a  two  column 
radiator.  Column  4  gives  the  radiation  as  determined 
by  Rule  3,  the  volume  rule,  the  volumes  of  the  rooms 
being  taken  from  Table  XX.  Column  5  gives  the  radia- 
tion that  would  actually  be  used.  The  quantities  in  col- 
umn 3  are  obtained  as  follows:  Assume  the  average 
temperature  of  the  water  in  the  radiator  is  170°.  The 
temperature  in  the  room  is  70°,  the  difference  is  100°. 
The  rate  of  transmission  as  given  in  Table  XXX,  line  4, 
is  1.50  B.  t.  u.  The  total  transmission  per  square 
foot  per  hour  is,  then,  1.50X100=150  B.  t.  u.  Di- 
viding the  heat  lost  from  the  room,  column  2,  by  150, 
or  the  loss  for  each  square  foot  of  radiation,  will  give 
the  results  in  column  3,  the  number  of  square  feet  of 
radiation  required.  In  column  4  the  radiating  surface 
has  been  determined  by  the  volume  rule,  Rule  3,  and 
shows  the  inconsistency  of  this  method  of  figuring,  though 
it  is  a  method  very  commonly  used.  This  method 
should  never  be  used  except  as  a  check.  When  the 
volume  rule  shows  very  much  larger  results  than  the 
other  rules  it  is  well  to  add  surface  to  the  radiator  to 
allow  for  heating  the  air  in  the  room.  This  has  been 
done  in  column  5.  In  regard  to  proportioning  of  ra- 
diation one  can  never  trust  absolutely  to  his  figures  and 
should  always  carefully  compare  his  results  with  the 
room  and  its  exposure  and  use  his  judgment  in  regard 
to  radiation  that  seems  desirable. 


126 


CHAPTER  VIII. 

HOT  WATER  BOILERS  AND  PIPING. 

Hot  Water  Boilers. — Hat  water  boilers  are  prac- 
tically the  same  as  steam  boilers.  Any  good  form  of 
steam  boiler  may  be  changed  to  a  hot  water  boiler  by  fill- 
ing the  steam  space  with  water  and  allowing  the  water 
to  go  in  at  the  lowest  point  of  the  boiler  and  go  out  at 
the  highest  point  of  the  boiler.  In  boilers  especially  de- 
signed for  hot  water  heating  no  space  is  left  over  the 
tubes,  the  whole  boiler  shell  being  filled  with  tube  sur- 
faces. This  makes  the  hot  water  boiler  more  compact 
for  the  same  amount  of  heating  capacity  than  the  steam 
boiler.  The  circulation  in  the  hot  water  boilers  is  prob- 
ably slower  than  in  steam  boilers  and  there  is  much  less 
local  circulation.  The  cold  water  enters  from  the  bot- 
tom, passes  over  the  tubes  and  leaves  at  the  top  of  the 
boiler.  The  heat  transmitted  per  square  foot  of  surface 
is  practically  the  same  in  steam  and  hot  water  boilers. 
The  proportions  of  heating  surface  to  grate  surface  and 
of  grate  surface  to  chimney  area  may  be  taken  the  same 
for  hot  water  as  for  steam. 

In  large  hot  water  systems  the  ordinary  fire  tube  boil- 
er is  used.  The  principal  modification  of  the  boiler 
would  be  to  fill  the  steam  space  with  tubes  and  make 
the  return  opening  same  size  as  the  steam  opening. 
For  residence  work  cast  iron,  sectional  boilers  are  usu- 
ally used  and  these  are  suitable  for  all  similar  work,  ex- 
cept where  high  pressure  is  used.  In  high  pressure  hot 
water  heating,  cast  iron  boilers  are  not  permissible,  as 
these  boilers  are  not  usually  made  to  withstand  pressures 
exceeding  20  pounds.  A  pressure  of  20  pounds  corre- 

127 


Notes         on          Heating         and         Ventilation 

spends  to  a  water  column  46  feet  high  and  this  is  about 
the  height  of  an  ordinary  four-story  building.  It  is  not 
desirable  to  use  cast  iron  boilers  in  buildings  more  than 
three  stories  high,  above  that  height  wrought  iron  boil- 
ers should  be  used  so  as  to  withstand  the  static  pressure 
due  to  the  height  of  the  water.  Cast  iron  boilers  would 
not  be  suitable  for  hot  water  systems  using  a  closed  tank 
and  having  the  water  under  pressure.  Boilers  for  these 
systems  are  usually  made  to  withstand  safely  a  pressure 
of  100  pounds  per  square  inch.  The  proportions  of  cast 
iron  boilers  for  hot  water  heating  are  given  in  Table 
XXXIII.  In  this  table  the  rating  of  the  boiler  does  not 
include  the  piping.  In  selecting  the  boiler  the  square 
feet  of  radiation  equivalent  to  the  piping  must  be  added 
to  the  square  feet  of  radiator  surface.  In  the  average 
house  these  boilers  will  carry  .6  of  their  rating  in  actual 
radiation,  exclusive  of  piping,  provided  the  piping  is 
covered  with  some  good  grade  of  pipe  covering. 

Hot  Water  Piping. — In  designing  a  hot  water 
piping  system  the  most  important  consideration  is  the 
resistance  of  the  piping.  The  resistance  of  the  piping 
should  be  almost  the  same  for  each  radiator  at  the  same 
level  and  the  friction  of  the  piping  system  should  be 
kept  as  low  as  practicable. 

DEFINITION  OF  TERMS  USED. — The  different  parts  of 
the  piping  system  referred  to  will  have  the  following 
meaning : 

FLOW  MAINS  AND  RISERS.— The  flow  mains  and  flow 
risers  are  those  portions  of  the  piping  system  which 
carry  hot  water  from  the  boiler  to  the  radiator.  The 
word  flow  always  refers  to  the  hot  side  of  the  system. 

RETURN  MAINS  AND  RETURN  RISERS. — The  terms  re- 

128 


Notes         on         Heating         and         Ventilation 

turn  mains  and  return  risers  refer  to  piping  which  re- 
turns the  cold  water  from  the  radiator  to  the  boiler. 

EXPANSION  TANK. — The  expansion  tank  is  a  vessel 
partly  filled  with  water  and  partly  filled  with  air,  which 
allows  for  the  variation  of  the  volume  of  water  in  the 
system  with  the  changes  of  the  temperature  of  the  water. 
In  the  open  tank  system  this  tank  is  situated  at  the 
highest  point  of  the  system.  In  the  closed  tank  system 
it  may  be  located  anywhere  in  the  building. 

TABLE  XXXIII.— PROPORTION  OP  CAST  IRON  HOT  WATER 

BOILERS. 
SQ  Ft.  of 

Radiation        Sq.  Ft.  of  Sq.  Ft.  of 

Boiler            Heating  Grate  Size  of  Pipe  Smoke 

will  Carry.       Surface.  Surface.  Connections.  Flue. 

150  25  1  2  8 

230    ....30  1.3  2  8 

375   40  1.6  2%  9 

500   60  2.5  2^s  9 

860  80  3.3  3  9 

1,300    120  5.0  3%  10 

2,000   160  6.5  4  11 

2,500. 200  8.5  5  or  2-3^  12 

3,000  250  10.0  6  or  2-4  14 

3,500 280  11.5  6  or  2-4  16 

4,000 330  13.5  6  or  2-5  18 

5,000 400  16.5  7  or  2-5  26 

6,000 500  20  8  or  2-6  22 

7,000 575  23  8  or  2-6  24 

8,000 650  26.5  2-7  or  3-5  26 

9,000 750  30  2-7  or  3-5  26 

10,000   800  33.5  2-8  or  2-6  28 

11,000 900  36.5  2-8  or  2-6  28 

PITCH. — The  pitch  of  the  pipe  refers  to  its  inclina- 
tion from  the  horizontal. 

LEGS  OF  THE  SYSTEM. — The  flow  main  is  often  termed 
the  hot  leg  of  the  system  and  the  return  main  the  cold 
leg  of  the  system. 

Systems  of  Piping. — Four  systems  of  piping  are 
used — the  multiple  circuit  system,  the  single  circuit  sys- 
tem, the  overhead  system,  and  the  single  pipe  system. 

MULTIPLE  CIRCUIT  SYSTEM. — This  system  is  the  one 
most  used  and  is  sometimes  called  the  standard  system 
of  piping.  This  system  is  shown  in  Fig.  51.  The  flow 

129 


Notes         on          Heating         and         Ventilation 

main  rises  from  the  top  of  the  boiler  to  a  convenient 
height  just  below  the  basement  ceiling  so  as  to  allow 


Fig.   51. 

for  pitch  towards  the  boiler  of  not  less  than  y2  an  inch 
in  10  feet.     This  main  or  mains  is  carried  around  the 

130 


Notes         on          Heating         and         Ventilation 

basement  so  as  to  supply  the  risers.  Too  many  risers 
should  not  be  taken  from  one  set  of  mains,  as  the  radiat- 
ors at  the  end  will  be  too  much  cooled.  The  main 
return  is  parallel  to  the  flow  main  and  of  the  same  size. 
The  open  expansion  tank  is  placed  at  least  3  feet  above 
the  last  radiator  and  should  be  connected  to  the  nearest 
riser.  The  connection  to  the  expansion  tank  should  be 
at  the  bottom  of  the  tank.  In  this  system  the  branches 
from  the  flow  main  usually  supply  only  one  radiator 
on  the  first  floor,  a  separate  branch  being  run  to  the. 
radiato'rs  on  the  second  and  third  floors.  At  the  points 
A  and  B,  Fig.  51,  where  the  riser  branches  to  go  to  the 
second  floor,  the  risers  offset.  This  is  done  to  prevent 
too  rapid  circulation  in  the  radiators  above  the  first  floor, 
the  tendency  being  for  the  second  floor  radiators  to  take 
all  the  water  and  prevent  circulation  in  the  first  floor  ra- 
diators. This  is  a  reason  why  it  is  preferable  to  connect 
first  and  second  floor  radiators  separately  to  the  flow 
main.  The  circulation  in  the  hot  water  system  depends 
upon  the  vertical  weight  of  the  system.  The  higher  the 
main  the  more  rapid  the  circulation.  This  makes  it  neces- 
sary to  put  additional  turns  in  the  risers  going  to  the  up- 
per floors  or  add  to  the  resistance  in  the  piping  system  so 
as  to  make  the'  resistance  to  each  floor  proportional  to  the 
effective  head  producing  circulation  at  that  floor. 

SINGLE  CIRCUIT  SYSTEM. — In  the  single  circuit  sy$- 
tem,  as  shown  in  Fig.  52,  the  water  flows  directly  to 
the  radiator  from  the  boiler  through  a  pipe  to  which 
no  other  radiator  is  connected  and  is  returned  to  the 
boiler  by  a  separate  pipe.  A  large  number  of  these  cir- 
cuits may  be  connected  to  one  boiler,  each  one  being  en- 
tirely separate  from  the  other..  This  is  one  of  the  earliest 
forms  of  piping  systems  used  for  hot  water  work.  _',  It 

131 


Notes         on          Heating         and         Ventilation 

gives  good  results  but  is  expensive  to  install  and  makes 
an   extremely   complicated  piping  system. 


Fig.   52. 

OVERHEAD  SYSTEM. — The  overhead  system  is  shown 
in  Fig.   53.       In  this  system  the  flow  main   is  carried 

132 


Notes          on          Heating 


and 


Ventilation 


directly  from  the  boiler  to  the  highest  point  in  the  sys- 
tem, usually  the  attic.     From  this  flow  main  risers  ex- 


Fig.  53. 

tend  to  the  basement  and  connect  to  the  main  return. 
This  system  is  sometimes  modified  as  shown  in  Fig.  54. 

133 


Notes 


o  n 


Heating         and          Ventilation 


Fig.    54. 


In  this  case  the  riser  in 
both  flow  and  return  main 
to  the  radiator  takes  its 
supply  at  a  point  near  the 
level  of  the  radiator  and 
delivers  the  water  at  a 
point  below  the  level  of 
the  radiator  in  the  same 
main.  One  objection  to 
this  arrangement  is  the 
fact  that  the  radiators  on 
the  upper  floor  will  be 
considerably  warmer  than 
the  radiators  on  the  lower 
floors  and  where  this  sys- 
tem is  installed  larger  ra- 
diators should  be  used  on 
the  lower  floors.  It  has  the 
advantage  of  simplicity. 

Open  and  Closed  Cir- 
cuits.— In  the  systems  de- 
scribed, with  the  excep- 
tion of  Fig.  54,  the  circu- 
lation from  flow  to  return 
main  takes  place  through 
the  radiators.  This  is 
what  is  termed  an  open 
circuit.  In  the  open  cir- 
cuit system,  where  two  or 
three  radiators  are  closed 
of,  the  resistance  to  cir- 
culation is  greatly  in- 


creased and  the  system  will  be  slow  to  circulate  when 
the  radiators  are  opened.    This  may  be  avoided  by  con- 


134 


Notes          on          Heating         and         Ventilation 

necting  up  the  piping  system  as  shown  in  Fig.  55.  The 
closed  circuit  system  is  particularly  desirable  in  large 
buildings,  especially  buildings  having  very  long  hori- 
zontal mains. 

Single  Pipe  System. — In  this  system  the  hot  water 
main  acts  as  both  flow  and  return  main,  the  radiators 
being  connected  on  tbe  two-pipe  systems  as  shown  in 


Fig.   55. 

Fig.  56.  It  is  necessary  in  the  single-pipe  hot  water 
system  to  make  the  mains  very  large  in  diameter,  as 
the  current  in  them  must  be  relatively  slow.  In  this  sys- 
tem the  hot  water  passes  along  the  top  of  the  main  and 
the  cold  water  passes  along  the  bottom  of  the  main. 
It  is  necessary,  then,  that  the  flow  riser  going  to  the  radi- 
ator be  connected  to  the  top  of  the  main  and  the  return 
riser  coming  from  the  radiator  be  connected  to  the  bot- 
tom of  the  main.  The  main  itself  is  usually  installed  on 
a  closed  circuit,  as  shown  in  Fig.  56.  The  single-pipe 

1S5 


Notes          on          Heating          and          Ventilation 

system  of  distribution  has  not  been  extensively  used  and 
has  not  great  advantage  over  the  standard  system  of 
piping. 


Fig.   56. 

Velocity  of  Flow. — As  previously  stated,  the  hot 
water  system  should  be  so  designed  that  the  resistance 
of  flow  to  each  radiator  should  be  proportional  to  the 
force  producing  flow.  The  water  will  always  seek  the 

136 


Notes         on          Heating         and         Ventilation 

path  of  least  resistance,  so  that  the  radiators  having  the 
smallest  pipe  resistance  will  receive  the  largest  quantity 
of  water,  and  radiators  having  the  largest  pipe  resistance 
will  be  proportionally  colder.  A  series  of  experiments 
have  been  made  at  the  University  of  Michigan  to  de- 
termine the  velocity  of  water  in  a  hot  water  heating  sys- 
tem under  actual  conditions  of  operation  with  full  sized 

TABLE    XXXIV.— VELOCITY    OF    HOT    WATER  CIRCULATION 

(FEET  PER  SECOND). 

Height  of  — Difference  in  Temperature. — 

Circuit  in  Feet.                10.                         15.  20. 

5                            .135                           .39  .55 

10                            .19                             .56  .78 

15                            .235                           .69  .95 

20                            .27                             .79  1.09 

25                            .30    -                         .88  1.22 

30                            .31                             .96  1.34 

40                            .38                           1.11  1.53 

50                             .425                         1.25  1.74 

pipes  and  radiators.  The  actual  velocity  was  found  to 
vary  from  one-quarter  to  one-half  of  the  theoretical 
velocity,  depending  upon  the  difference  in  temperature 
between  the  hot  and  cold  leg  of  the  system.  In  Table 
XXXIV  the  actual  velocities  have  been  computed  from 
the  results  obtained  by  these  experiments  for  different 
heights  and  different  conditions  of  temperature. 

Resistance  of  Pipe  and  Fittings. — No  complete  set  of 
experiments  has  been  made  to  determine  the  resistance 
of  pipe  and  fittings.  The  University  of  Michigan  at 
the  present  time  is  making  a  series  of  experiments,  but 
these  have  not  yet  been  completed.  The  following  are 
the  ordinary  assumptions  that  have  been  made: 

TABLE   XXXV.— SIZE    OF  HOT   WATER  MAINS. 

Diameter  Total    Length  of  Circuit  In  Fe«t. 

of  mains.  50.  100.  200.  300. 

1  40  30 

1*4  60  45  30 

1H  90  60  40  30 

2  160  120  70  60 
2#  250  200  120  110 

3  350  300  200  190 
S%  500  400  330  250 

4  650  500  450  359 
4»*  900  700  650  500 

5  1,200  1,000  800  650 

6  1,500  1.200  1,200  1,000 

137 


Notes         on         Heating         and         Ventilation 

Resistance  of  standard  elbow=25  feet  of  pipe. 
Resistance  of  standard  tee=25  feet  of  pipe. 
Resistance  of  standard  return  bend— 35  feet  of  pipe. 
Resistance  of  the  ordinary  radiator  connection  from  the 

flow  main  through  the  radiator  to  the  return  main  is 

equivalent  to  about  100  feet  of  pipe. 

Size  of  Pipe. — The  size  of  pipe  may  be  figured  by 
assuming  the  actual  velocity  due  to  the  head  and  calcu- 
lating the  size  required  to  carry  a  given  amount  of 
water.  This  is  usually  done  in  large  buildings.  In 
smaller  buildings  it  is  customary  to  follow  the  rules 
used  in  good  practice. 

TABLE  XXXVI. 

The  capacity  of  mains  100  ft.  long-,  expressed  in  the  number  of 
square  feet  of  hot-water  radiating  surface  they  will  supply,  the 
radiators  being-  placed  in  rooms  at  70°  Fahr.,  and  20°  drop  being 
assumed. 

Diameter  of  Two   pipe     One    pipe     Overhead    Overhead   Two-Pipe 
Pipes.          up  Feed       up  Feed    Open    tank.    Closed    Open    tank. 
Open    tank.  Open    tank.  Tank.      Indirect, 

12  in.  above 

Direct  Direct  Direct  Direct 

Inches.          Radiation.  Radiation.  Radiation.     Radiation,      boiler. 

1% 75  45  127  250  48 

1^ 107.  65  181  335  69 

2 200  121  339  667  129 

2H 314  190  533  1,060  202 

3 540  328  916  1,800  848 

3^ 780  474  1,334  2,600  502 

4 1,060  645  1,800  3,350  684 

5 1,860  1,130  3,150  6,200  1,200 

6 2,960  1,800  5,000  9,800  1,910 

7 4,280  2.700  7.200  13,900  2,760 

8 5,850  3,500  9,900  19,500  3,778 

Table  XXXV  gives  the  pipe  sizes  of  the  mains  to 
supply  different  quantities  of  direct  radiation  at  different 
distances  from  the  boiler.  In  establishing  the  size  of 
the  risers  it  is  customary  to  start  with  a  riser  the  same 
size  as  the  radiator  connection  and  carry  the  riser  down 
to  the  floor  below  where  the  next  radiator  connects.  If 
the  radiator  does  not  exceed  60  feet  in  size,  add  one  pipe 
size  to  the  pipe. 

138 


Notes          on          Heating         and         Ventilation 


Table  XXXVI  gives  the  radiation  that  may  be  carried 
by  different  sized  pipes  in  the  different  systems. 

Table  XXXVII  gives  the  size  of  risers  for  various 
quantities  of  radiation  on  different  stories. 

TABLE  XXXVH. 

The  capacity  of  risers  expressed  in  the  number  of  square  feet  of 
direct  hot  water  radiating1  surface,  they  will  supply  the  radiators 
being  placed  in  room  at  70°  Fahr.  and  20°  drop  being  assumed: 

Closed  Tank 
Overhead 
System. 
Drop  risers, 
Second 
Floor. 


Diameter  of 
Riser 


Open  Tank  System. 


Inches. 


1... 

1%. 

¥.. 


First 

Floor. 

33 

71 

100 

187 

292 

500 


46 
104 
140 
262 
410 
755 


Third 
Floor. 
57 
124 
175 
325 
492 
875 

Fourth 
Floor. 
64 
142 
200 
375 
580 
1,000 

not  exceed- 
ing 4  floors. 
48 
112 
160 
300 
471 
810 

A ftUU  (00  OIO  l.UUU 

The  following  are  radiator  tappings  for  hot  water 
radiators : 

Radiators  containing  40  sq.  ft.  and  under 1  inch 

Radiators  containing  above  40  sq.  ft.  and  not  exceeding 

72  sq.  ft 1^4  inch 

Radiators  containing  above  72  sq  ft \y2  inch 

Air  Valves,  Pitch  and  Support  of  Pipes. — Hot  water 
piping  should  be  pitched  towards  the  boiler  so  that  the 
water  may  be  drained  out  of  the  system  at  the  boiler  and 
arrangements  should  be  made  so  that  the  water  can  be 
drained  to  the  sewer.  This  is  necessary  on  account  of 
freezing  if  the  plant  is  not  kept  in  operation.  The  pip- 
ing should  be  supported  the  same  as  for  steam  pipes, 
with  supports  about  every  10  feet.  Care  should  be  taken 
that  the  pipes  are  straight,  as  any  sudden  elevation  in 
the  pipe  will  form  a  pocket  in  which  air  will  collect,  and 
this  collecting  of  air  in  the  pocket  will  prevent  the  flow  of 
water.  An  accumulation  of  air  in  the  pipe  will  stop  the 
circulation  almost  as  effectively  as  a  valve.  The  expan- 

139 


Notes         on          Heating         and         Ventilation 

sion  of  pipes  by  heat  must  also  be  taken  care  of  as  in 
the  steam  system.  All  branches  going  from  the  piping 
system  and  supplying  radiators  below  the  level  of  the 
mains  should  come  off  the  bottom  of  the  main,  so  as 
to  prevent  air  accumulating  and  sealing  the  pipe. 

All  radiators  and  high  points  in  the  mains  where  air 
will  collect  should  be  provided  with  air  valves. 

There  are  special  air  valves  made  for  hot  water  work. 
These  will  be  described  later. 


CHAPTER  IX. 

VENTILATION. 

Necessity  of  Ventilation. — The  necessity  of  ventila- 
tion, that  is,  of  renewing  the  air  in  a  closed  room,  is  due, 
first  to  the  vitiation  of  the  air  by  the  products  of  respir- 
ation from  the  persons  in  the  room ;  second,  to  the  prod- 
ucts of  combustion  from  artificial  illumination;  third,  to 
the  heat  generated  by  persons  and  lights  in  the  room ; 
and,  fourth,  to  the  presence  of  gases  from  chemical 
processes. 

In  a  small  house  or  a  small  school  building  ventilation 
is  very  easily  produced  by  methods  which  employ  natural 
draft,  such  at  hot  air  furnaces,  steam  and  indirect  radi- 
ators. In  all  systems  using  natural  draft,  the  force  of 
the  draft  depends  upon  the  difference  of  the  temperature 
between  the  air  inside  and  that  outside  the  flue.  Where 
this  difference  amounts  to  only  30°  or  40°  the  difference 
in  the  weights  of  the  columns  of  air  is  so  small  that  the 
force  producing  draft  is  very  light  and  may  be  easily 
overcome  by  external  conditions.  In  larger  buildings 
it  is  not  possible  to  use  natural  draft  as  the  flues  be- 
come excessive  in  size  and  are  not  certain  enough  in  their 
operation.  This  has  led  to  the  use  in  school  buildings 
and  other  public  buildings  of  a  forced  system  of  ventil- 
ation in  which  the  circulation  is  produced  by  a  fan  or 
system  of  fans. 

The  perfectness  of  the  ventilation  in  a  room  is  ordi- 
narily determined  by  the  amount  of  carbonic  acid  gas. 
Carbonic  acid  gas  is  not  poisonous  in  itself.  Its  in- 
jurious effects  are  produced  entirely  by  the  reduction  of 
the  oxygen  in  the  room.  There  are,  however,  other  in- 

141 


Notes         on          Heating         and         Ventilation 

jurious  gases  given  off   from  the  body,   together  with 
the  carbonic  acid  gas. 

Products  of  Respiration.— The  lungs  take  in  oxy- 
gen from  the  air,  which  combines  with  the  tissues  of 
the  body,  forming  the  products  of  combustion  which  are 
given  off  by  the  excretory  organs — lungs,  skin,  etc.  The 
principal  excretions  removed  by  the  lungs  are  carbonic 
acid  gas,  water  vapor  mixed  with  other  gases  and  some 
animal  matter.  These  excretions,  together  with  excre- 
tions from  the  skin,  produce  a  disagreeable  odor  and 
may  be  poisonous.  The  average  man  when  sitting  still 
consumes  in  breathing  from  19  to  25  cubic  feet  of  air 
per  hour,  and  when  exercising  from  26  to  35  cubic  feet 
per  hour.  The  amount  of  carbon  dioxide  and  water 
vapor  given  off  per  hour  by  human  beings  is  given  in 
Table  XXXVIII. 

TABLE  XXXVIII.— AIR  POLLUTION   TESTS. 
Subject  to  Test.  At  Work.  At  Rest. 

Temp.  Humid.  CO2      H2O     Temp.  Humid.  CO2        H2O 
Deg.F.  P.C.  Cu.Ft.  Grains.  Deg.F.  P.C.  Cu.Ft.  Grains. 

Laborer 45         81        1.515         2.03          69        20         .551         1.12 

Laborer     ..77        47        1.423         8.05          78        26        .586         2.55 

Clerk    64         44         1.331         1.768         69         29       1.141         1.19 

Draughtsman   ..69         41        1.61          1.61  ..         ..  ...          .... 

Average  man 66        63        .412        1,365 

Woman 600          

Boy ..          -48 

Girl 39  

Products  of  Combustion. — The  products  of  com- 
bustion from  the  sources  of  heating,  such  as  grates, 
stoves,  etc.,  are  drawn  off  by  the  chimney,  but  the  prod- 
ucts of  combustion  from  the  lights  in  a  room  pass  di- 
rectly into  the  room.  Lights  give  off  carbonic  acid  gas, 
watery  vapor,  and  traces  of  sulphuric  acid.  Table 
XXXIX  gives  the  consumption  of  combustibles  and  the 
generation  of  carbon  acid  gas  by  ordinary  forms  of 
lighting.  The  table  is  given  for  each  normal  candle 

power. 

142 


Notes         on         Heating         and         Ventilation 

TABLE    XXXIX.— POLLUTION    BY    LIGHTING. 

Consumption  of  Com-  Carbonic  Acid 

bustible  per  C.  P.  per  C.  P.  in 

Source.                              in  Cu.  Ft  Per  Hour.  Cu.  Ft.  Per  Hour. 

Gas— Fishtail   burner    802— .527  .494— .304 

Gas— Argand  burner 0     —.445  .254 

Gas— Welsbach  burner 053— .024  .030— .057 

Petroleum,  round  burner Gals.     .00050  .112 

Petroleum,  small  flat  burner. Gals.     .00198  .335 

Wax  candles    Oz.     .271  .417 

Paraffine  candle   Oz.     .324  .459 

Chemical  Processes. — The  products  of  chemical 
operations  should  never  accumulate  in  a  room  so  that 
the  odor  is  perceptible.  In  some  industrial  processes  it 
is  almost  impossible  to  avoid  a  certain  amount  of  con- 
centration of  the  gases.  In  such  a  case  the  chemical 
products  should  be  sufficiently  diluted  with  fresh  air 
so  as  not  to  produce  injurious  effects  upon  the  occupants 
of  the  room. 

Table  XL  gives  the  relative  dilution  required  for  dif- 
ferent gases  in  cubic  feet  per  100  cubic  feet  of  air. 

TABLE  XL.— AIR  DILUTION. 

Detrimental  Effect  Occurs 

in  Several  Hrs.  in  %-l  Hr. 

Iodine  vapors 00005  .0003 

Chlorine  or  bromide  vapors 0001  .0004 

Muriatic  acid   001  .005 

Sulphuric  acid   .005 

Sulphureted  hydrogen .02 

Ammonia    01  .03 

Carbonic  Oxide 02  .05 

Carbonic  acid  1.00  8.00 

Carbureted  hydrogen : 6.56  gr. 

Generation     of     Heat     by     Human     Beings. — The 

amount  of  heat  generated  by  a  human  being  varies  with 
age,  activity  and  temperature  of  the  surrounding  air. 
The  average  amount  of  heat  given  off  by  an  adult  is 
about  400  B.  t.  u.  per  hour,  and  by  a  child  about 
half  that  amount,  or  200  B.  t.  u.  per  hour.  Of  400 
B.  t.  u.  given  off  by  human  beings  about  30  per  cent 
is  lost  by  contact  of  air  and  about  43  per  cent  by  radi- 
ation, the  balance  is  lost  by  exhalation  and  other  losses. 

143 


Notes         on         Heating         and         Ventilation 

Comparing  this  with  the  average  steam  radiator,  we  see 
that  a  child  is  equal  to  about  eight-tenths  of  a  square  foot 
of  radiation  and  an  adult  man  is  equal  to  about  one  and 
eight-tenths  of  a  square  foot  of  radiation.  This  becomes 
a  very  important  point  in  the  heating  of  large  halls,  par- 
ticularly if  they  are  very  crowded  and  have  very  little 
external  wall  space,  as  the  heat  given  off  by  the  persons 
in  the  room  may  be  more  than  sufficient  to  warm  the 
room,  which  will  necessitate  providing  for  the  removal 
of  this  heat  from  the  room. 

Generation  of  Heat  by  Illumination. — Ordinarily 
the  heat  given  off  by  electric  lights  is  so  small  as  to  be 
negligible,  but  where  oil  lamps,  candles,  or  gas  lights 
are  used,  the  heat  given  off  is  appreciable,  except  in  the 
case  of  the  Welsbach  burner,  which  gives  off  relatively 
a  small  amount  of  heat.  The  ordinary  fish-tail  burner 
is  equal  to  about  one  and  four-tenths  square  feet  of  radi- 
ation. 

Table  XLI  gives  the  heat  generated  by  different 
sources  of  illumination  per  candle  power  per  hour. 

TABLE  XLI.— HEAT   GIVEN   OFF  BY  ILLUMINANTS. 

Total  B.  T.  U.'s 
Source.  Given  Off. 

Gas — Fishtail  burner   313 

Gas — Argand  burner  198 

Gas — Welsbach  burner   32 

Petroleum   158 

Incandescent  lamp   14 

Arc  lamp 2.5 

Changes  of  Air  Necessary. — In  order  that  the  air 
in  a  room  occupied  by  human  beings  may  be  reasonably 
pure  it  should  be  diluted  with  fresh  air.  The  amount  of 
the  dilution,  except  where  chemical  processes  are  to  be 
considered,  is  usually  determined  by  the  per  cent  of  car- 
bon dioxide  present,  which  is  assumed  to  be  proportional 
to  the  products  of  respiration.  The  carbon  dioxide  itself 

144 


Notes         on         Heating         and         Ventilation 

is  not  injurious,  but  it  serves  as  an  indication  of  the 
presence  of  other  injurious  substances.  It  is  usually 
assumed  that  carbon  dioxide  is  uniformly  distributed 
throughout  the  room.  This,  however,  is  not  strictly  true, 
as  carbon  dioxide  is  a  very  heavy  gas  and  naturally  ac- 
cumulates at  the  floor.  Air  that  contains  more  than  ten 
parts  of  carbon  dioxide  to  each  10,000  parts  of  air  pro- 
duced by  exhalation  is  of  an  unhealthful  quality.  Seven 
parts  in  10,000  is  ordinarily  considered  the  minimum 
limit  of  ventilation.  The  effects  of  poor  ventilation  are 
usually  shown  when  the  carbon  dioxide  exceeds  six  parts 
in  10,000  parts.  The  following  rule  may  be  used  to 
determine  the  necessary  amount  of  air  that  should  be 
supplied  to  a  room :  Multiply  the  number  of  sources  of 
carbon  dioxide  by  the  amount  of  carbon  dioxide  given 
off  from  each  source.  Multiply  the  result  by  10,000  and 
divide  by  4.  This  will  give  the  minimum  amount  of 
ventilation  to  be  allowed  per  person.  For  satisfactory 
ventilation  divide  by  3.  Pure  air  is  found  to  contain 
about  3  parts  of  carbon  dioxide  in  10,000. 

This  may  be  expressed  as  follows : 

Let  S=cu.  ft.  carbonic  acid  from  each  source  per  hour. 
n= number  of  sources. 

a— allowable  limit  of  CO,  in  10,000  cu:  ft.  of  air. 
A=the  cu.  ft.  of  air  to  be  supplied. 

nS 

Then  A=10,000 

a— 4 

a  should  not  exceed  7  and  a  equals  10  is  the  sanitary 
limit. 

For  example,  take  a  hall  containing  400  adults,  giving 
off  (from  Table  XXXVIII)  .58  cu.  ft.  of  CO2  per  hour. 


145 


Notes         on         Heating         and         Ventilation 

Then  to  determine  the  amount  of  air  necessary  substitute 
in  the  above  formula 
400X.58 

A=10,000 -  solving 

6—3 
A=  770,000  cu.  ft.  per  hour. 

Ordinary  Assumption  for  Change  of  Air. — The 
amount  of  air  necessary  is  usually  determined  by  allow- 
ing each  person  in  the  room  so  many  cubic  feet  of  air 

TABLE  XLJI.— CHANGE  OF  AIR  NECESSSARY. 

Hospitals    3,600  cu.  ft.  per  person 

Barracks  and  workshops   3,000  cu.  ft.  per  person 

Schools    2,400  cu.  ft.  per  person 

Churches,  theaters  and  audience  halls 2,000  cu.  ft.  per  seat 

Office    rooms    1,800  cu.  ft. 

Toilet  and  bath  rooms 2,400  cu.  ft.  per  fixture 

Dining  rooms  1,800  cu.  ft.  per  person 

per  hour.  The  changes  of  air  ordinarily  allowed  are 
given  in  Table  XLII. 

These,  figures  in  the  above  table  give  sufficient  air  so 
that  the  air  in  the  room  will  remain  continuously  pure, 
even  though  occupied  all  the  time.  When  less  than  these 
amounts  are  used  there  is  danger,  if  the  buildings  are 
very  tight,  that  the  rooms  may  become  foul.  The  figures 
given  above  are  seldom  realized  in  practice,  except 
where  the  fan  system  of  ventilation  is  used.  In  school 
buildings  using  an  indirect  system  the  amount  of  air 
allowed  per  child  seldom  exceeds  1,000  cubic  feet  of 
air  per  hour. 

Another  method  that  is  sometimes  used  in  figuring 
ventilation,  particularly  for  smaller  buildings,  is  to  allow 
so  many  changes  of  air  per  hour.  In  rooms  seldom  oc- 
cupied allow  the  air  to  be  changed  about  once  per  hour. 
In  living  rooms  about  one  and  a  half  to  two  times 
per  hour.  In  toilet  rooms  four  to  five  times  per  hour. 
In  restaurants,  where  smoking  is  allowed,  from  five  to 

146 


Notes         on         Heating         and         Ventilation 

six  times  per  hour.  In  extreme  cases  the  change  of  air 
is  sometimes  as  high  as  ten  times  per  hour.  It  is  diffi- 
cult, however,  to  change  the  air  in  a  room  very  rapidly 
without  producing  drafts. 

Effects  of  Poor  Ventilation. — The  effects  of  poor 
ventilation  have  been  frequently  tested  in  schools  where 
for  a  short  time  the  ventilation  has  been  cut  off.  The 
pupils  at  first  complain  of  being  cold,  and  it  is  found 
necessary  to  raise  the  temperature  of  the  room  from  70° 
to  80°  before  the  occupants  of  the  room  are  warm. 
This  is  no  doubt  due  to  the  reduction  in  vitality  owing 
to  the  impurity  of  the  air,  and  a  lack  of  oxygen  in  the 
lungs.  After  the  ventilation  has  been  cut  off  for  a 
period  of  from  20  to  30  minutes,  the  pupils  begin  to 
complain  of  headache.  If  the  ventilation  is  cut  off  much 
longer  it  is  necessary  to  dismiss  some  pupils  on  account 
of  headache. 

Systems  of  Ventilation. — For  small  residences  and 
small  buildings  where  it  is  not  possible  to  go  to 
any  great  expense  for  an  elaborate  system  of  ven- 
tilation, the  best  form  of  heating  giving  adequate 
ventilation  is  the  hot  air  furnace.  In  large  houses 
where  it  is  not  possible  to  apply  the  hot  air  sys- 
tem, the  best,  system  is  indrect  radiators,  either  steam 
or  hot  water.  In  still  larger  buildings  where  the  flues 
have  a  large  resistance  and  it  is  necessary  to  supply 
air  in  large  quantities,  the  only  feasible  system  of  dis- 
tributing air  is  by  mechanical  means.  The  usual  system 
employed  is  to  draw  the  air  through  a  series  of  steam 
coils  into  a  tempered  air  chamber.  In  this  chamber  are 
located  the  fans.  The  fan  or  fans  deliver  the  air  through 
heating  coils  into  the  building.  Systems  similar  to  this 

147 


Notes         on          Heating         and         Ventilation 


have  been  used  where  the  coils  have  been  replaced  by 
hot  air   furnaces. 

Systems  of  ventilation  using  mechanical  draft  give 
very  satisfactory  results  if  properly  installed  and  allow 
of  great  latitude  in  the  arrangement  of  the  plant.  Before 
taking  up  the  details  of  the  systems  of  ventilation  it  is 
well  to  consider  certain  fundamental  facts  in  the  science 
of  ventilation. 

Air  Inlets  and  Outlets. — The  arrangement  of  inlet 
and  outlet  registers  in  a  room  should  be  given  very 


Fig.   57. 


careful  consideration.  They  should  be  so  placed  as  to 
avoid  drafts  and  to  insure  uniform  circulation  through- 
out the  room.  Their  position  should  be  such  that  the 
air  cannot  pass  directly  from  inlet  to  outlet  flue.  The 
creation  of  drafts  may  be  avoided  by  bringing  the  air 
in  at  very  low  velocities,  particularly  where  the  air 

148 


Notes          on          Heating 


and 


Ventilation 


enters  so  as  to  strike  the  occupants  of  the  room.  The 
velocity  passing  through  the  registers  should  not  exceed 
300  feet  per  minute ;  if  it  is  admitted  just  over  the  heads 
and  where  the  current  of  air  strikes  a  person,  it  should 
not  exceed  150  feet  per  minute.  Where  the  air  is 
brought  in  so  that  it  cannot  strike  the  occupants  of  the 
room  the  velocity  of  air  through  the  registers  may  be  as 
high  as  400  feet  per  minute. 


The  most  satisfactory  arrangement  for  most  rooms 
is  shown  in  Fig.  57.  In  this  figure  the  inlet  register  is 
shown  near  the  ceiling.  The  hot  air  leaving  this  regis- 
ter rises  to  the  ceiling,  passes  along  the  ceiling  to  the 
cold  window  surfaces,  where  it  is  cooled  and  drops  to 
the  floor;  passes  along  the  floor  and  out  the  vent  flue. 
The  inlet  register  is  usually  located  about  8  feet  above 

149 


Notes         on          Heating         and         Ventilation 


the  floor  and  the  outlet  register  from  4  to  6  inches 
above  the  floor,  just  sufficient  to  avoid  dust  and  dirt 
being  swept  into  it.  Where  the  current  of  air  leaving 
the  inlet  register  is  liable  to  be  centered  in  one  point 
in  the  room  it  is  well  to  put  a  diffusing  register  on  the 
air  inlet  so  that  the  air  will  be  distributed  in  a  number 


Fig.  59. 

of  streams  in  different  directons  throughout  the  room. 
This  arrangement  of  inlet  and  outlet  registers  is  the 
usual  one  for  school  buildings.  It  is  preferable  to  have 
the  inlet  and  outlet  register  on  the  inside  walls  opposite 
the  window  surfaces  and  both  registers  on  the  same 
wall.  This,  however,  is  not  absolutely  necessary.  The 
inlet  and  outlet  registers  should  never  be  on  the  outside 
walls.  Where  the  inlet  register  is  placed  on  the  floor 

150 


Notes         on         Heating         and         Ventilation 

and  the  outlet  register  at  the  ceiling  then  the  air  com- 
ing from  the  inlet  register  will  pass  directly  to  the 
outlet  register  and  a  large  proportion  of  the  heated  air 
be  lost;  in  addition  there  will  be  very  little  circulation 
of  air  in  the  room,  as  shown  in  Fig.  58. 

In  rooms  for  restaurant  purposes,  where  smoking  is 
allowed  or  in  smoking  rooms  or  in  kitchens,  the  air 
must  be  taken  off  the  ceiling,  as  the  foul  air,  being 
warmer,  rises  to  the  ceiling.  In  this  case  it  is  necessary 
to  bring  the  ventilating  air  in  at  the  baseboard,  at  a 
very  low  velocity  and  at  a  number  of  places  and  take  the 
air  out  at  definite  points  near  the  ceiling,  as  shown  in 
Fig.  59.  In  theaters  and  churches  special  means  must 
be  employed  for  securing  ventilation.  It  is  customary 
to  admit  the  air  in  a  large  number  of  places.  Some- 
times this  is  done  by  means  of  a  large  number  of  small 
registers  placed  directly  under  the  seats.  Care,  how- 
ever, must  be  used  in  doing  this  to  avoid  drafts.  An- 
other method  is  to  employ  a  large  number  of  openings 
around  the  sides  of  the  room.  The  air  is  usually  taken 
off  near  the  stage  at  the  lowest  point  in  the  auditorium. 
There  should  be  provided  in  all  auditoriums  some  means 
of  taking  the  air  off  the  ceiling,  as  oftentimes  the  heat 
given  off  by  the  occupants  of  the  room  is  more  than 
sufficient  to  heat  the  room,  and  in  addition  we  have  the 
heat  given  off  by  the  sources  of  illumination.  This  heat 
can  be  best  taken  care  of  at  the  ceiling  line,  which  is 
naturally  the  warmest  point  in  the  room. 


151 


CHAPTER  X. 

DESIGN  OF  HOT  AIR  HEATING  SYSTEM. 

Design  of  Hot  Air  System. — In  a  hot  air  furnace 
the  cold  air  from  the  outside  is  passed  over  heated  iron 
surfaces,  usually  enclosed  in  galvanized  iron  or  brick 
walls.  The  space  between  the  walls  and  hot  surfaces 
of  the  furnace  is  connected  to  the  outside  air  at  the 
bottom  and  at  the  top  to  the  flues  leading  to  the  rooms. 
The  amount  of  air  circulating  through  the  furnace  will 
depend  upon  the  temperature  of  the  hot  air  leaving  the 
furnace  and  the  height  and  resistance  of  the  flues.  In 
order  that  the  air  in  a  room  may  be  quickly  replaced  by 
warm  air  it  is  necessary  that  the  room  be  provided  with 
a  foul  air  flue. 

A  great  many  of  the  difficulties  that  have  been  expe- 
rienced with  the  hot  air  system  as  ordinarily  installed 
are  due  to  the  sharp  competition  in  business,  which  has 
resulted  in  the  erection  of  plants  of  inferior  workman- 
ship and  design.  One  of  the  commonest  mistakes  is 
the  installation  of  a  furnace  much  too  small  to  do  the 
work  properly.  The  result  of  putting  in  a  small  fur- 
nace is  that  the  fire  must  be  continually  crowded  so  that 
the  heating  surface  is  at  high  temperature  and  a  large 
amount  of  the  heat  of  the  coal  is  wasted  in  excessive 
stack  temperature. 

The  hot  air  system  with  natural  draft  should  not  be 
used  in  houses  where  the  horizontal  portion  of  the  hot 
air  flues  would  exceed  20  feet  in  length.  In  very  large 
houses  two  or  more  furnaces  may  be  used  to  avoid 
excessive  pipe  resistance. 


152 


Notes          on          Heating         and          Ventilation 

Hot  Air  Furnaces. — Hot  air  furnaces  are  as  varied 
in  types  as  are  steam  boilers.  They  are  made  either 
of  cast  iron  or  steel.  It  is  difficult  to  decide  between 
the  merits  of  these  two  materials.  Cast  iron  is  less  lia- 
ble to  be  rapidly  deteriorated  by  rust  when  the  boiler 
stands  in  the  summer,  but  it  is  more  easily  broken  either 
by  misuse  or  shrinkage  strains  in  the  castings.  There 
is  no  essential  difference  between  the  metals  in  their 
conducting  capacity  as  applied  in  these  furnaces. 

It  is  very  important  to  see  that  the  furnace  is  so  con- 
structed that  the  joints  between  the  fire-box  and  hot-air 
chamber  are  tight,  so  that  the  air  entering  the  rooms 
may  not  be  mixed  with  gases  of  combustion.  This  is  one 
of  the  most  difficult  things  to  prevent  in  the  hot  air 
furnace.  Joints  should  be  as  few  as  possible  and  ver- 
tical joints  should  be  avoided.  The  introduction  of  mois- 
ture into  the  air  passing  through  the  furnace  is  an  im- 
portant consideration  and  will  be  treated  in  a  separate 
paragraph. 

The  builders  rate  their  furnaces  at  about  their  maxi- 
mum capacity.  The  rating  being  expressed  as  the  num- 
ber of  cubic  feet  of  building  volume  the  furnace  will 
heat.  In  selecting  a  furnace  it  is  wise  to  have  25  to  50 
per  cent  excess  capacity  in  the  furnace  over  the  build- 
er's rating. 

The  fire  pot  of  a  furnace  should  be  slightly  conical 
in  shape  and  should  be  large  enough  to  contain  sufficient 
fuel  to  last  eight  hours.  The  rate  of  combustion  on  the 
grate  should  be  taken  at  not  to  exceed  4  pounds  of  coal 
per  hour.  A  high  temperature  of  combustion  is  usually 
desirable  for  the  best  economy,  but  the  stack  gases  should 
not  exceed  500°. 

The  air  space  between  the  furnace  and  the  outside 

153 


Notes         on          Heating         and         Ventilation 

casing  should  have  at  least  25  per  cent  more  cross- 
sectional  area  than  the  leader  pipes  taken  from  it.  A 
furnace  should  be  proportioned  so  that  the  air  leaving  it 
should  not  exceed  180°  in  temperature. 

There  should  be  one  square  foot  of  grate  for  every  30 
to  50  square  feet  of  heating  surface  in  the  furnace.  Each 
square  foot  of  heating  surface  may  be  assumed  to  give 
off  1,000  to  1,500  B.  t.  u.  per  hour. 

A  furnace  should  be  provided  with  some  form  of 
shaking  and  dumping  grate  which  is  easily  cleaned.  In 
addition  to  draft  doors  admitting  air  below  the  grates, 
the  furnace  is  usually  provided  with  a  check  damper 
in  the  smoke  pipe.  The  draft  door  and  check  damper 
are  arranged  so  that  they  may  be  controlled  by  chains 
situated  in  some  convenient  point  in  the  room  above. 

Necessity  of  Supplying  Moisture  to  Heated  Air. — 

It  is  very  important  that  air  after  being  heated  by  the 
furnace  pass  over  the  surface  of  a  pan  of  water  so  that 
it  can  take  up  moisture.  One  pound  of  air  at  32°  F. 
will  hold  in  the  form  of  a  vapor  .003  of  a  pound  of 
water,  and  at  150  degrees  it  will  hold  .22,  or  about  70 
times  as  much.  If  then  we  take  air  saturated  with 
moisture  at  an  outside  temperature  of  32  degrees  and 
heat  it  up  to  150  degrees  we  have  increased  its  capacity 
for  moisture  70  times.  On  entering  the  rooms  if  the 
air  has  not  been  given  opportunity  to  take  up  moisture 
it  will  take  it  up  from  the  objects  of  the  room.  This 
drying  effect  of  the  air  injures  the  furniture  and  wood- 
work and  affects  the  persons  occupying  the  room,  pro- 
ducing a  dry  throat  and  a  feeling  of  cold  due  to  rapid 
evaporation  from  the  skin. 

The  usual  method  of  overcoming  this  is  to  have  a  pan 

154 


Notes         on          Heating         and         Ventilation 

filled  with  water  situated  in  the  furnace  near  the  fire- 
box. This,  however,  is  the  wrong  end  of  the  furnace 
to  place  the  pan,  as  the  air  entering  is  coolest  at  this 
point.  The  water  should  be  added  to  the  air  as  it  leaves 
the  furnace.  In  some  hot  air  installations  every  pipe 
leaving  the  furnace  has  a  trough  in  it,  which  is  filled 
with  water,  and  from  this  water  the  air  takes  up  its 
moisture. 

Cold  Air  Duct. — The  cold  air  supplied  to  the  fur- 
nace is  usually  taken  from  one  of  the  basement  win- 
dows and  brought  to  the  furnace  through  a  tile  or 
wooden  duct  lined  with  galvanized  iron;  where  a  tile 
duct  is  used  it  is  placed  below  the  level  of  the  cellar 
floor.  The  cold  air  should  be  taken  from  the  side  of 
the  house  that  is  subject  to  the  prevailing  winds.  It  is 
sometimes  desirable  to  have  cold  air  ducts  leading  to 
different  sides  of  the  house,  so  that  the  supply  of  cold 
air  may  be  taken  from  the  windiest  side.  The  cross- 
section  of  the  cold  air  duct  should  be  80  per  cent  of  the 
area  of  the  hot  air  leaders  leaving  the  furnace. 

It  is  well  to  provide  some  means  of  recirculation  of 
the  air  in  the  house  through  the  furnace.  The  air  for 
recirculation  is  usually  taken  from  the  Hall.  If  it  is 
desired  to  recirculate  partially  and  take  the  balance  of 
the  air  from  outside,  the  recirculating  pipe  should  be 
brought  to  the  furnace  separately,  and  a  deflecting  plate 
placed  in  the  air  space  under  the  furnace.  If  this  is  not 
done  the  air  will  come  in  from  the  outside  and  may  pass 
up  the  recirculating  pipe  instead  of  going  to  the  furnace. 
If,  however,  the  recirculating  pipe  is  only  to  be  used 
when  the  cold  air  pipe  from  outside  is  closed,  then  the 
recirculating  pipe  can  be  conducted  into  the  cold  air 

155 


Notes         on          Heating         and         Ventilation 

pipe  directly.  In  this  case  the  cold  air  pipe  and  recircu- 
lating pipe  must  both  be  provided  with  dampers.  The 
cold  air  pipe  should  have  at  least  three-fourths  of  the 
combined  areas  of  the  hot  air  pipes. 

It  is  a  common  error  to  make  the  recirculating  pipe  of 
a  furnace  system  too  small.  The  recirculating  pipe 
should  be  not  less  than  three-fourths  the  area  of  the 
cold  air  pipe.  It  is  better  to  have  it  equal  in  area 
to  the  cold  air  pipe. 

Hot  Air  Leaders  and  Flues. — The  furnace  should 
be  centrally  located,  or  if  the  coldest  winds  come  from 
a  certain  direction,  it  can  be  located  more  on  that  side 
of  the  house  from  which  the  cold  winds  come.  The  hot 
air  flues  leading  from  the  furnace  should  be  as  short 
and  direct  as  possible;  long  horizontal  pipes  should  be 
avoided.  Horizontal  pipes  should  pitch  sharply  towards 
the  furnace,  three-quarter  inch  to  the  foot  is  good  prac- 
tice. All  hot  air  pipes  should  have  nearly  equal  resist- 
ance to  the  passage  of  the  air.  The  hot  air  flues  should 
have  as  few  and  as  easy  turns  as  possible.  They  should 
never  be  placed  in  the  outside  walls.  Uptake  flues  of 
any  kind  in  outside  walls  seldom  draw  satisfactorily. 
The  hot  air  flue  should  enter  the  room  in  most  cases 
opposite  the  largest  exposed  glass  surface  or  some  dis- 
tance from  it.  The  circulation  of  air  in  the  room  would 
be  best  if  the  hot  air  entered  near  the  ceiling.  The  prin- 
cipal objection  to  this  is  that  the  register  in  the  wall 
is  apt  to  blacken  the  wall  and  it  does  not  allow  people 
to  warm  themselves  over  it.  Floor  registers  are  very 
objectionable  as  they  always  serve  as  receptacles  for  all 
kinds  of  rubbish  and  sweepings. 

Dampers   should  be  provided  in  all  pipes  leading  to 

156 


Notes         on         Heating         and         Ventilation 

rooms  above  the  first  floor.  If  all  the  registers  are  pro- 
vided with  dampers  there  is  danger  of  burning  the  fur- 
nace, due  to  shutting  off  all  the  passages  for  removing 
hot  air  and  preventing  circulation  in  the  furnace.  It  is 
good  practice  to  have  no  valve  in  the  hall  register  so  one 
pipe  will  always  be  open. 

Proportions  of  Hot  Air  Flues. — The  velocity  of  air 
for  first  floor  leaders  may  be  calculated  as  three  or 
four  feet  per  second,  second  floor  four  to  five  feet  per 
second,  third  floor  and  floors  above  five  to  six  feet  per 
second.  The  flues  leading  to  the  second  and  third  floor 
room  may  have  a  velocity  as  high  as  400  feet  per  minute. 

In  the  best  installations  the  leads  and  flues  are  double 
walled  with  asbestos  between  the  walls.  The  cross- 
sectional  area  of  all  the  leaders  should  be  from  1.1  to  1.5 
times  the  area  of  the  grate. 

The  registers  should  be  proportioned  so  as  to  give 
a  velocity  of  two  to  three  feet  per  second  on  the  first 
floor  and  three  to  four  feet  per  second  on  the  floors 
above.  The  effective  area  of  'the  ordinary  registers  is 
about  50  per  cent  of  the  actual  area,  taking  outside  di- 
mensions. 

H.  B.  Carpenter,  in  a  paper  before  the  Society  of 
Heating  and  Ventilating  Engineers  (Transactions,  vol.  5, 
p.  77),  gives  the  following  rule  for  finding  the  cubic 
feet  of  air  passing  through  pipes  per  minute : 

To  the  first  floor  multiply  the  area  in  inches  by  1.25. 

To  the  second  floor  multiply  the  area  in  inches  by  1.66. 

To  the  third  floor  multiply  the  area  in  inches  by  2.08. 

It  is  good  practice  to  figure  on  changing  the  air  in  the 
principal  rooms  five  times  per  hour  in  hot  air  heating. 

Foul  Air  Flues. — The  foul  air  flues  should  be  placed 

157 


Notes         on          Heating         and         Ventilation 

in  the  inside  walls  and  with  foul  air  registers  at  the 
baseboard.  The  reason  being  that  the  hot  air  entering 
the  room  opposite  the  window  surfaces  rises  to  the 
ceiling,  passes  along  the  ceiling  to  the  windows  and  is 
cooled.  It  then  drops  to  the  floor  line,  passes  along 
the  floor  and  out  the  foul  air  register.  The  hot  air  reg- 
ister should  be  a  sufficient  distance  from  the  foul 
air  register  so  that  the  hot  air  will  not  pass  directly  to 
the  foul  air  flue.  A  cheap  foul  air  flue  can  be  made  by 
having  a  register  in  the  baseboard  opening  into  the 
spaces  between  the  studs,  selecting  a  space  that  is  open 
to  the  attic,  a  ventilator  is  placed  on  the  attic  space  and 
discharges  foul  air  out  of  doors.  No  two  rooms  should 
open  into  the  same  studding  space.  A  still  better  draft 
can  be  produced  by  extending  each  flue  separately  by 
galvanized  iron  pipe  to  the  ventilator.  If  no  ventilating 
flues  are  provided,  it  is  very  difficult,  especially  if  the 
house  is  tight,  to  get  a  proper  circulation  of  hot  air  from 
the  furnace;  you  cannot  put  hot  air  into  a  room  if 
there  is  no  provision  for  taking  cold  air  out. 

The  area  of  these  foul  air  flues  should'  be  not  less 
than  80  per  cent  of  that  of  the  warm  air  flues  and  they 
are  often  made  equal  in  area  to  the  area  of  the  warm 
air  flues. 

A  fireplace  makes  one  of  the  best  forms  of  foul  air 
flue.  In  a  house  well  provided  with  fireplaces,  it  is 
often  not  necessary  to  provide  any  other  foul  air  flues. 

General  Proportions  of  Hot  Air  Systems. — The  size 
of  the  hot  air  flue,  vent  flue,  hot  air  register,  heating 
surface  and  grate  surface  in  the  furnace  is  given  in 
Table  XLI//  This  table  is  given  for  rooms  of  average 
proportion  and  under  average  conditions. 

158 


Notes         on         Heating         and         Ventilation 


TABLE  XLIIL— PROPORTIONS  OF  HOT  AIR  HEATING  SYSTEM. 


Contents  of  Room  in  Cubic  Feet 
First  Floor  — 
Diameter  hot  air  flue    in 

500 
6 

1,000 
8 

1,500 
9 

Diameter  foul  air  flue    in 

g 

g 

g 

Second  Floor  — 
Diameter  hot  air  flue    in.. 

6 

7 

g 

Diameter  foul  air  flue    in  . 

6 

7 

g 

Grate  area  in  furnace,   SQ 

in     .  .  . 

25 

50 

75 

Heating  surface  in  furnace 

sq    ft 

5 

10 

15 

2,000        2,500        3,000        3,500 
10             11             12             13 
10             11             12             13 
9             10             11             11 
8               9               9             10 
100           125           150           175 
20             25             30             35 

4,000 
14 
14 
12 
10 
200 
40 

5,000 
16 
16 
14 
12 
250 
50 

6,000 
17 
17 
15 
12 
300 
62 

8,000 
20 
20 
18 
14 
850 
.5          80 

10,000 
24 
24 
20 
16 
400 
100 

The  following  assumptions  have  been  made  the  above 
table:  Temperature  outside  air,  0  degree;  temperature 
of  air  in  the  room,  70  degrees;  changes  of  air  in  the 
room,  three  times  per  hour. 

Velocity  of  air  in  hot  air  flues,  1st  floor,  3  ft.  per 
second. 

Velocity  of  air  in  hot  air  flues,  2nd  floor,  4  ft.  per 
second. 

Velocity  of  air  in  four  air  flues,  1st  and  2nd  floors,  3  ft. 
per  second. 

Temperature  of  air  entering  the  room,  160  degrees. 

Proportion  of  grate  surface  to  heating  surface,  1  to  30. 

Pounds  of  coal  burned  per  square  foot  of  grate  sur- 
face per  hour,  3. 

Suggestions  for  Operating  Hot  Air  Furnaces. — The 

temperature  of  the  rooms  should  be  regulated  by  the 
drafts  of  the  furnace  as  much  as  possible.  The  heating 
surfaces  of  the  furnace  should  never  be  brought  to  a 
red  heat.  If  it  is  necessary  to  do  this  to  keep  the  rooms 
warm,  the  furnace  is  too  small. 

Ashes  should  be  frequently  removed  from  the  furnace, 
as  an  accumulation  of  ashes  may  burn  out  the  grate. 
Never  shake  the  fire  more  than  is  necessary  to  expose 

159 


Notes          on          Heating          and          Ventilation 

the  red  coals  to  the  ash  pit.  The  furnace  should  be 
cleaned  at  least  once  a  year.  The  water  pan  of  the  fur- 
nace should  be  kept  full  of  water. 

ROUGH  RULES  FOR  HOT  AIR  SYSTEM. 

1.  The  volume  of   the   house   divided  by   50   equals 
square  feet  of  heating  surface  in  furnace  radiator. 

2.  The  volume  of  the  house  divided  by   20   equals 
the  number  of  square  inches  of  grate  area  in  the  furnace. 

3.  Divide  the  volume  of  the   room   by  20   and   the 
square  root  of  the  quotient  will  be  the  diameter  of  the 
furnace  pipe  for  the  first  floor  room.     For  second  floor 
rooms  divide  the  volume  by  25  and  the  square  root  of  the 
quotient  will  be  the  diameter  of  the  furnace  pipe. 

Example  of  Hot  Air  System. — As  an  example  of 
the  hot  air  system  applied  to  the  ordinary  dwelling,  take 
the  same  house  that  was  used  as  an  example  of  direct 
steam  heating.  The  heat  lost  from  the  rooms  would  be 
the  same  as  in  the  case  of  direct  steam.  As  an  example 
of  an  individual  room  take  the  parlor. 

From  Table  XX  we  see  that  the  volume  of  the  parlor 
is  1,665  cubic  feet  and  the  heat  lost  10,395  B.  t.  u. 
per  hour.  In  figuring  the  heating  system  for  the  parlor 
the  following  assumption  will  be  made:  The  hot  air 
enters  the  room  at  160°.  Cold  air  enters  the  furnace 
at  0°.  The  temperature  in  the  room  is  70°.  Then  the 
air  entering  the  room  is  reduced  in  temperature  160 — 
70=90°.  Each  pounds  of  air  on  having  its  temperature 
reduced  90°  would  give  up  .2375X90=21.4  B.  t.  u. 
Then  there  will  have  to  be  introduced  into  the  room  to 
supply  heat  lost  from  the  room  10,395-^21.4=485  pounds 
of  air  per  hour.  At  atmospheric  pressure  a  pound  of 

160 


Notes         on         Heating         and         Ventilation 

air  occupies  approximately  13  cubic  feet,  hence  485 
pounds  of  air  is  equal  to  6,300  cubic  feet.  This  is  the 
amount  of  air  which  must  be  delivered  to  the  room  per 
hour;  6,300  cubic  feet  of  air  per  hour  is  equal  to  1.75 
cubic  feet  per  second.  Allowing  a  velocity  of  3  feet  per 
second,  the  area  of  the  pipe  would  be  1.75-^3  —  .58  square 
feet,  which  is  equivalent  to  84  square  inches,  or  approxi- 
mately the  area  of  a  pipe  10.5  inches  in  diameter.  To 
warm  the  air  going  to  the  parlor  would  require  485 X 
.2375X160=18,500  B.  t.  u.  In  a  similar  way  the  same 
quantities  have  been  calculated  for  the  other  rooms. 
Except  that  for  the  second  floor  room,  a  velocity  of  4  feet 
per  second  has  been  allowed. 

TABLE  XLIV. 

B.t.u.  Cu.  ft.       Diam- 

Volume  lost.  B.t.u.         of  air        eter 


First  Floor. 
Parlor 

of 

room. 

1  665 

from  room 
per  hour. 

10,305 
7,035 
7,350 
10,300 
7,035 

10,050 
7,560 
7,035 
7,455 
3,150 
5,250 
2,730 

given  air 
per  hour. 

18,500 
12,500 
12,800 
18,000 
12,500 

17,900 
13,400 
12,500 
13,300 
5,600 
9,400 
4,800 

entering    of  hot 
room,     air  pipe. 

6,300            10i/£ 
4,350              9 
4,600              9 

6,250             10% 
4,350               9 

6,200,               9 
4,750               8 
4,400               8 
4,650               8 
1,850               G 
3,300               7 
1,750               6 

Sitting  room 

2  100 

Dining  room  

.  .1,640 

Kitchen  

.  .1,610 

Hall  

1  210 

Second  Floor. 
West  Alcove  
Alcove    
South    chamber.  .  . 
North    chamber.  .  . 
Bath       

...1,320 

.  .  .     810 
...1,560 
.  ..1,440 
410 

East  chamber.... 
Halls 

.  .  .     880 
88 

151,200 

Column  3  of  Table  XLIV  shows  the  heat  which  is  left 
by  the  air  in  the  room.  Column  4  shows  the  heat  used 
to  warm  the  air  entering  the  room.  The  difference  be- 
tween these  two  columns  is  the  heat  lost  up  the  ventilat- 
ing flues.  This  loss  should  not  be  charged  against  the 
hot  air  furnace,  but  should  be  considered  as  the  loss 
that  must  be  charged  to  ventilation.  The  loss  is  about 
44  per  cent  if  the  temperature  of  the  outside  air  is  at  0° 

161 


Notes 


o  n 


Heating          and          Ventilation 


and  the  temperature  of  the  air  entering  the  room  is  160°. 
As  the  temperature  of  the  outside  air  or  the  incoming 
air  is  increased  proportionately  more  heat  enters  the 
room  and  this  loss  becomes  less.  During  the  average 
winter  weather  the  outside  air  is  35°,  in  which  case  the 
per  cent  of  loss  by  ventilation,  that  is,  through  the  ven- 
tilating flues,  is  about  30  per  cent. 


Fig.  60. 


Summing  up  column  4  of  the  table  gives  the  heat 
required  to  warm  the  air  entering  the  entire  house  in 
zero  weather  or  151,200  B.  t.  u.  If  we  assume  that  80 


162 


Notes          on          Heating          and          Ventilation 

per  cent  of  the  coal  goes  into  the  heated  air,  then  there 
will  be  required  from  the  coal  151,200-=-. 8=188,500 
B.  t.  u.  per  hour.  A  good  anthracite  coal  contains  about 
13,500  B.  t.  u. ;  then  in  zero  weather  this  house 
would  use  188,500-^-13,500=14  pounds  of  coal  per  hour. 
As  the  average  loss  from  a  house  during  the  heating 
season  is  approximately  50  per  cent  of  the  loss  during 
zero  weather,  the  average  consumption  of  coal  in  this 
house  for  the  heating  season  would  be  14X -5=7.00 
pounds  of  coal  per  hour.  Assuming  the  furnace  to  be 
operated  34  hours  per  day  and  200  days  per  year,  the 
coal  consumption  for  this  house  would  be  7  X  24X200 -r- 
2,000=16.8  tons.  Fig.  60  shows  a  cross  section  of  a 
house  with  the  hot  air  system  installed. 


163 


CHAPTER  XI. 

FAN  SYSTEM  OF  HEATING. 

Where  it  is  necessary  to  introduce  large  quantities 
of  air  into  a  building  for  the  purpose  of  ventilation  a 
natural  system  of  circulation  is  out  of  the  question  and 
it  is  necessary  to  force  the  air  into  the  building  by  some 
mechanical  device.  This  is  usually  done  by  means  of  a 
steel  plate  blower  which  delivers  the  air  with  sufficient 
pressure  to  force  the  air  into  all  rooms  in  the  building. 
The  pressure  required  in  the  average  building  does  not 
usually  exceed  one-quarter  ounce.  The  mechanical  sys- 
tem of  ventilation  has  the  additional  advantage  that  its 
operation  is  entirely  independent  of  the  heating  of  the 
building  and  the  building  maybe  ventilated  as  easily  in 
the  summer  as  in  the  winter.  The  natural  system  of 
ventilation  depends  entirely  upon  the  air  in  the  flues 
being  heated,  and  during  the  summer  periods  the  system 
is  inoperative. 

Systems  of  Fan  Heating. — There  are  two  general 
schemes  of  fan  heating,  one  in  which  the  air  is  heated 
to  a  temperature  higher  than  that  in  the  room,  so  that 
it  furnishes  enough  heat  to  supply  the  heat  lost  from  the 
walls  and  windows,  as  well  as  to  furnish  air  for  ventila- 
tion. In  the  other  system  the  heat  loss  from  walls  and 
windows  is  supplied  by  direct  radiation  situated  in  the 
room  and  the  fan  supplies  only  the  necessary  amount 
of  air  for  ventilation.  In  the  latter  system  the  air  for 
ventilation  is  supplied  at  about  the  temperature  to  be 
maintained  in  the  room.  The  first  system,  in  which  all 
the  heat  is  supplied  by  means  of  a  fan,  is  most  applica- 

164 


Notes          on          Heating         and         Ventilation 

ble  in  buildings  that  must  be  heated  and  ventilated  both 
night  and  day.  Hospitals  and  asylums  are  buildings  of 
this  class.  It  has  certain  disadvantages,  however.  When 
a  room  has  very  large  glass  surfaces  it  is  almost  impos- 
sible with  this  system  to  prevent  strong  cold  drafts  com- 
ing down  along  the  window  surfaces.  The  system  is 
in  many  cases  wasteful.  In  order  to  heat  a  building  it  is 
often  necessary  to  admit  more  air  than  is  required  for 
the  purpose  of  ventilation,  and  all  the  heat  put  into  the 
air  to  raise  the  temperature  of  the  outside  air  to  the 
temperature  of  the  room  is  lost.  On  the  other  hand, 
this  system  requires  but  one  system  of  heating,  which 
makes  it  less  expensive  to  'install. 

The  second  system  mentioned,  where  direct  radiation 
and  a  fan  are  both  used,  is  most  applicable  in  buildings 
that  require  ventilation  only  part  of  the  time.  Schools, 
factories,  office  buildings  are  buildings  that  may  be.  in- 
cluded in  this  class.  While  the  buildings  are  filled  with 
occupants  the  fan  system  is  operated ;  as  soon  as  the 
occupants  leave  the  building  the  fan  system  is  closed  and 
the  building  kept  warm  by  means  of  direct  radiation. 
The  building  is  thus  kept  warm  at  a  minimum  expendi- 
ture for  fuel.  There  is  no  necessity  of  introducing  into 
the  building  more  air  than  is  necessary  for  ventilation. 
But  the  system  is  expensive  to  install,  as  it  involves 
installing  two  separate  systems  of  heating.  This 
system  is  being  more  and  more  favorably  considered, 
however,  in  connection  with  the  class  of  buildings  men- 
tioned. 

General  Arrangement  of  the  Fan  System. — The  us- 
ual arrangement  of  the  fan  system  is  shown  in  Fig.  61. 
The  air  is  drawn  first  through  a  series  of  tempering  coils 

165 


Notes         on         Heating         and         Ventilation 

shown  at  A.  Then  it  enters  a  tempered  air  chamber 
in  which  is  located  the  fan.  This  delivers  the  air  through 
a  series  of  heating  coils  B  into  the  hot  air  chamber. 
From  this  hot  air  chamber  the  individual  rooms  in  the 
buildings  take  their  heat.  The  tempered  coils  are  usually 
designed  to  heat  the  air  to  about  70°.  The  fan  takes 
this  air  at  70°  and  passes  it  to  the  heating  coils.  After 
leaving  the  heating  coils  the  temperature  of  the  air  is 
from  130°  to  140°.  Where  the  air  is  used  for  ventilation 
only  the  heating  coils  are  omitted  and  the  air  is  deliv- 


Fig.   61. 

ered  by  the  fan  from  the  tempered  air  chamber  directly 
to  the  room. 

Quantity  of  Air  to  Be  Supplied. — The  quantity  of 
air  to  be  supplied  to  each  room  will  depend  upon  the 
system  of  heating  employed.  If  the  heating  is  done  en- 
tirely by  fan  enough  air  must  be  admitted  so  that  the 
heat  left  by  the  air  will  be  sufficient  to  heat  the  room. 
In  audience  and  school  rooms  the  amount  of  air  necessary 
to  supply  proper  ventilation  is  usually  sufficient  for  heat- 
ing. In  offices  and  living  rooms  more  air  will  have  to 

166 


Notes          on          Heating          and          Ventilation 

be'  supplied  in  order  to  heat  the  room  than  would  be 
necessary  for  purposes  of  ventilation.  Roughly  speak- 
ing, if  the  number  of  cubic  feet  of  air  supplied  to  the 
room  per  hour  is  four  times  the  cubic  contents  of  the 
room  the  room  will  be  heated,  providing  the  air  be  sup- 
plied at  not  less  than  140°.  In  a  system  where  direct 
radiation  is  used  to  supply  losses  from  walls  and  win- 
dows only  enough  air  is  introduced  to  supply  the  neces- 
sary ventilation.  The  amount  of  air  necessary  can  be 
determined  by  rules  previously  given  under  the  head  of 
Ventilation. 

Size,  Speed  and  Horsepower  of  Fan. — In  most  cases 
the  type  of  fan  known  as  the  steel  plate  blower  or  multi- 
vane  fan  is  best  adapted  to  the  work  of  fan  heat- 
ing. The  theory  of  this  fan  has  been  discussed  by 
Weisbach  and  Lindner  in  their  treatises,  also  by  vari- 
ous writers  in  the  Transaction  of  the  Society 
of  Heating  and  Ventilating  Engineers.  The  results 
derived  are  difficult  of  application.  The  following 
general  statement  may  be  made,  however:  The  dis- 
charge capacity  of  a  fan  depends  upon  the  speed  of 
the  fan  tips,  the  size  of  the  fan  blades,  and  the  size  of 
the  discharge  openings.  As  the  discharge  opening  of 
the  fan  is  decreased  the  velocity  of  the  air  leaving  the 
fan  increases  and  the  pressure  of  air  in  the  fan  case 
increases  until  we  get  to  the  maximum  pressure  that 
can  be  produced  by  a  certain  velocity  of  fan  tips.  This 
will  occur  when  the  area  of  the  outlet  equals  the  effec- 
tive area  of  the  fan  blades.  This  is  the  point  at  which 
the  fan  delivers  the  maximum  amount  of  air  correspond- 
ing to  the  pressure  for  a  given  speed.  If  we  further 
reduce  this  discharge  outlet  the  pressure  in  the  fan  case 

167 


Notes         on         Heating         and         Ventilation 


remains  constant,  the  quantity  of  air  discharged  is  re- 
duced and  the  power  to  drive  the  fan  is  reduced. 

TABLE    XLV.— FAN    CAPACITIES. 

Speeds,  Capacities  and  Horse  Powers  of  "A  B  C"  Steel  Plate  Fans 
of  Varying  Revolutions. 


eo    70    so    eo    100  no  I  iao  1*0  leo  iso  200  220 


NOTE 

These  figures  guaranteed  to 
be  correct  with  the  resistance 
ordinarily  found  in  heating 
work. 


The  theoretical  relations  connecting  the  pressure  of 
the  air,  the  quantity  of  air  delivered,  power  to  drive  the 
fan  and  the  speed  can  be  stated  briefly  as  follows :  The 
quantity  of  air  delivered  is  proportional  to  the  peri- 
pheral velocity  of  the  fan  tips  and  to  the  width  of  the 

168 


Notes          on          Heating         and          Ventilation 


fan  tips.  The  pressure  produced  is  proportional  to  the 
square  of  the  peripheral  velocity  of  the  fan  tips  and 
the  power  necessary  is  proportional  to -the  cube  of  the 
peripheral  velocity  of  the  fan  tips  and  to  the  quantity 

TABLE    XLVL— FAN     EFFICIENCY    UNDER    VARYING     PRES- 
SURES. 

Breeds,  Capacities  and  Horse  Powers  of  "A  B  C"  Steel  Plate  Fans 
of   Varying   Pressures. 


PRESSURES. 

Xoz. 

2740 
880 
.80 

*«, 

KM. 

1  oz. 

"•« 
385 

IX  01. 

1'i  oz. 

IK  01. 

2  ox. 

2'/,  01. 

So.. 

50 

CU.  FT. 
R.  P.  M. 
H.  P. 

3900 
540 
130 

4760 
659 
Mi 

•a? 

532 

6700 
930 
6.65 

7850 
1004 

8.22 

7750 
1075 
10.25 

8650 
1200 
14.38 

9620 
& 

60 

CU.  FT 

v>M- 

3550 
817 
1.03 

5040 
449 
2.05 

5490 
549 
3.42 

7100 
633 
4.95 

7910 
706 
6.84 

8700 

776 
8.54 

9410 

888 
10.60 

18750 
716 
1560 

10200 
895 
13.2 

~^ 
19.40 

11210 
1000 
18.45 

12330 
1100 
24.3 

70 

CU.  FT. 
R.  P.  M. 
H.  P. 

5220 
271 

Ltl 

7350 
883 
3.02 

9050 
471 
5.04 

10400 
542 
7.30 

11600 
605 
10.10 

12700 
663 
12.SU 

16500 
857 
27.20 

18000 

a 

21920 

825; 

43.2  ' 

27300 
734 
53.5 

80 

£.VSi 

H.  P. 

i 

^ 
3.65 

10940 
412 

6.08 

12550 

84£ 

142S 

12.15 

"85 
15.20 

16600 
186! 

17300 
6?2 
23.40 

22100 
5ftt 
29.10 

19890 
750 
83".80 

24750 
666 
40.70 

90 

CU.  FT. 
R.  P.  M. 
H.  P. 

7850 
211 
2.27 

11050 
299 
4.53 

18600 
366 
7.56 

15600 
421 
11.00 

17450 
470 
15.10 

19100 
515 
18.90 

20650 
557 
23.40 

100 

CU.  FT. 
R.  P.  M. 
H.  P. 

«tt 
2.76 

13500 
268 
5.52 

16500 
329 
9.20 

19050 
380 
13.35 

23600 
345 
16.60 

21300 
424 
18.42 

~T8 

22.U) 

23300 
464 
23.00 

25200 
502 

28.60 

27000 
537 
35.10 

"S 

49.60 

33000 
659 
65.2 

110 

CU.  F?. 
R.  P.  M. 
H.  P. 

"fS 
8.43 

16700 
244 

6.85 

"8 

1144 

"S 

2860 

31300 
456 
35.50 

33500 

44^ 

37500 
546 
61.7 

41200 
600 
81.2 

51800 
550 
102.1 

190 

CU.  FT. 
R.  P.  M. 
H.  P. 

15000 
159 
4.32 

21000 
224 

8.65 

25840 
274 
14.40 

29700 
816 
20.M) 

33200 
854 

28.80 

36400 
387 
36.00 

39400 
44.60 

42200 
448 

55.45 

47100 
500 

77.7 

140 

CU.  FT. 
R.  P.  M. 
H.  P. 

19800 
136 

5.72 

27900 
192 
11.42 

34200 
235 

19.00 

89400 
271 
27.60 

44000 
302 
38.10 

48200 
331 
47.60 

51200 
357 
59.00 

"S 

73.80 

63900 
439 
1027 

68400 
470 
185.5 

87500 
412 
172.0 

160 

CU.  FT. 
R.  P  M 
H.  P 

.25050 
118 
7.29 

35600 
168 
14.60 

43700 
206 
24.32 

50250 
237 
85.20 

56150 
48^ 

61500 
290 
160.75 

66500 
314 

75.30 

71250 
336 
93.50 

79200 
873 
134.0 

180 

CU.  FT. 
R.  P.  M. 
H.  P. 

31410 
106 
9.07 

44200 
1& 

54300 
18S 
30.24 

62700 
211 
43.80 

69700 
235 
60.48 

76700 
259 
75.5 

82700 
279 
93.6 

88400 
298 
116.20 

9VOOO 
834 
131.0 

108400 
214.0 

200 

CU.  FT. 
R.  P.  M. 
H.  P 

38000 
• 
11.02 

53700 
22^ 

3 

75700 
189 
53.8 

84950 
212 
73.5 

93000 
232 
92.0 

100500 
251 
114.0 

""a 

141.5 

120000 

»85 

134000 
330 
261.0 

280 

CU.  FT. 
R.  P.  M. 
H.  P. 

46800 
87 
13.48 

66300 
123 

27.00 

~7900<r 
112 
32.30 

80900 
150 

44.90 

93200 
173 
65.10 

104000 

£ 

113500 
211 
112.0 

123300 
•229 
139.0 

131400 
244 
173.0 

147100 
243I0 

161500 
300 
818.0 

194000 
275 
382.0 

240 

CU.  FT. 
R.  P  M. 
H.  P. 

56400 
80 
16.10 

WJ500 
137 
53.80 

112000 
15H 
78.00 

124800 
177 
1074 

136SOO 
194 
134.0 

147400 
209 
166.0 

158000 
224 
2060 

176100 
250 
290.0 

of  ai*  delivered.  Mr.  M.  C.  Huyett  gives  the  follow- 
ing approximate  rule  for  finding  the  capacity  of  a  fan : 
The  quantity  of  air  in  cubic  feet  delivered  per  revolu- 
tion is  equal  to  one-third  the  diameter  of  the  fan 
wheel  multiplied  by  the  width  of  the  blades  at  cir- 

169 


Notes         on          Heating         and         Ventilation 

cumference,  multiplied  by  the  circumference  of  the  fan 
wheel.  All  dimensions  expressed  in  feet. 

Professor  R.  C.  Carpenter  gives  the  following  rule 
for  determining  the  horsepower  required  by  the  fan: 
The  horsepower  required  for  the  fan  is  equal  to  the 
fifth  power  of  the  diameter  of  the  fan  wheel  in  feet 
multiplied  by  the  number  of  revolutions  per  second, 
divided  by  1,000,000  and  multiplied  by  one  of  the  fol- 
lowing coefficients — for  free  delivery,  30 ;  for  delivery 
against  1-ounce  pressure,  20 ;  for  delivery  against  2 
ounces  pressure,  10.  The  best  method  of  obtaining  the 
horsepower  to  drive  a  fan  and  the  capacity  of  the  fan 
is  by  reference  to  the  table. 

Table  XLV  gives  the  speed,  capacity  and  horsepower 
required  for  various  sized  fans  as  determined  by  the 
American  Blower  Co. 

Table  XLVI  gives  similar  results  for  different  sized 
fans  at  varying  pressure. 

Table  XLVII  gives  the  results  for  a  fan  of  the  multi 
vane  type,  such  as  the  Sirocco. 

The  table  should  be  made  use  of  in  the  following 
manner:  Having  determined  the  quantity  of  air  re- 
quired for  the  entire  building,  we  select  from  the  table 
a  fan  which  would  give  the  proper  capacity.  In  doing 
this  three  things  must  be  considered.  The  fan  must 
have  sufficient  capacity  to  deliver  the  amount  of  air 
required.  It  must  deliver  this  air  with  the  minimum 
horsepower,  and  it  must  rotate  with  sufficient  speed  to 
product  a  pressure  in  the  fan  system  sufficient  to  over- 
come the  resistance  of  the  piping.  It  is  always  possi- 
ble to  select  either  a  small  fan  driven  at  a  high  speed  or 
a  large  fan  driven  at  a  low  speed,  both  of  which  will 
deliver  the  same  capacity  of  air.  A  large  fan  may  be 

170 


Notes 


o  n 


Heating         and         Ventilation 


TABLE   XLVII. 

Speeds,    Capacities    and    Horse    Powers    of    Single    Inlet,    Standard 
Width   Fans  at   Various   Pressures. 


Figure.  Giren  Represent  Dynamic  Pn-«ure>  in  Ounce* 
FocVelod 


F«  Subc 


Deduct  28.8%. 


'of 
Fan* 

Diameter 
l£, 

JOi. 

i'Oi. 

JOi. 

10.. 

H0». 

1J  Oz. 

IJ-Oi. 

20*. 

2*0i. 

30,. 

00 

3 

CU.  FT. 
R.P.  M. 
B.  H.  P. 

38 
2290 
.005 

55 
3230 
013 

67 
3960 
.024 

77 
4580 
.037 

87 
5120 
.051 

95 

5600 
068 

102 
6050 
.085 

110 
6460 
105 

122 
7232 
145 

135 
7920 
190 

I 

«| 

CU.FT. 
R.P.M. 
B.  H.  P. 

87 
1524 
.011 

125 
2152 
030 

152 
2640 
.053 

175 
3048 
064 

197 
3400 
116 

215 
3732 
.153 

232 
4040 
.193 

250 
4304 

.238 

277 
4816 
.330 

305 

5280 
433 

1 

6 

CU.FT. 
R.P.  M. 
B.  H.  P. 

155 
1145 
.0185 

220 
1615 
052 

270 
1980 
.095 

310 
2290 
.147 

350 
2560 
205 

2800 
270 

410 
3025 
.34 

440 
3230 
.42 

490 
3616 
.58 

540 
3960 
.76 

li 

n 

CO.  FT. 

fc&S 

242 
915 
029 

344 
1290 
082 

422 
1585 
.149 

485 
1830 
.230 

548 
2050 
.320 

594 

2240 
.422 

640 
2420 
.532 

688 
2580 
656 

766 
2890 
.910 

844 
3170 
1  19 

II 

t 

8M 

B.  H.  P. 

350 
762 
.042 

500 
1076 
118 

610 
1320 
.216 

700 
1524 
333 

790 
1700 
.463 

860 
1866 
.610 

930 
2020 

1000 
2152 
.95 

1110 
2406 
1  32 

1220 
2640 
1.73 

2 

12 

CU.FT. 
R.P.  M. 
B.  H.  P. 

625 
572 
.074 

880 
808 
208 

1080 
990 
.381 

1250 
1145 
.588 

1400 
1280 

.82 

1530 
1400 
1.08 

1650 
1512 
1.36 

1770 
1615 
1.66 

!&° 
2.32 

2170 
1980 
3.05 

2* 

IS 

CU.FT. 
R.P.M. 

B.  a  P. 

975 
456 
.115 

1380 
645 
.326 

1690 
790 
.600 

1950 
912 
923 

2180 
1020 
1.29 

2400 
1120 
1.69 

2590 
1210 
2.14 

2760 
1290 
2.61 

3090 
1444 
3  65 

3390 
1580 
4.8 

3 

ie 

CU.  FT. 
R.P.  M. 
B.  H.P. 

1410 
381 
.167 

1990 
538 
470 

2440 
660 

.862 

2820 
762 
1.33 

3160 
850 
1.85 

3450 
933 
2  43 

3720 
1010 
3.07 

3980 
1076 
3.75 

4450 
1204 
5.25 

4880 
1320 
6.9 

31 

21 

CU.  FF. 
R.P.M. 
B.  H.  P. 

1925 
326 
.227 

2710 
462 
640 

•SB 

1.17 

3850 
652 
1  81 

4290 
730 
2  53 

4700 
800 
3  33 

5070 
864 
4.18 

5420 
924 
5.11 

6060 
1032 
7.15 

6620 
1130 
94 

4 

24 

CU.  Ff. 
R.P.  M. 
B.  H.  P. 

2500 
286 
.296 

3540 
404 

.832 

4340 
495 
1  53 

5000 
572 
2  35 

5600 
640 
3  28 

6120 
700 
4.32 

6620 
756 
5  44 

7060 
807 
6.64 

"8? 

93 

8680 
990 
12.2 

4* 

27 

CU.  FT. 

ft  5* 

3175 
254 
373 

4490 
359 
1.05 

*% 
1.94 

6350 
508 
2.98 

7100 
568 
4.16 

7780 
622 
5.48 

8400 
672 
6.90 

8980 
718 
8.44 

10050 
804 
11.8 

11000 
880 
15.5 

5 

H 

2V1 

B.  H.  P. 

3810 
228 
460 

5520 
322 
1  30 

6770 
395 
2.40 

7820 
456 

3.68 

8750 
510 
5.15 

"S 

6  75 

10350 
604 
8.53 

11050 
645 
104 

12350 
722 
14.5 

13550 
790 
19.1 

• 

• 

cu.  Fr. 

R.P.  M. 
B.  H.  P. 

5650 
190 

665 

7950 
269 
1  87 

9750 
3*2 

11300 
381 
5  30 

12040 
425 
740 

13800 
466 
9.72 

14900 
504 
12.25 

•us 

15  0 

17800 
602 
209 

19500 
660 
27.5 

7 

42 

CU.  FT. 
R.P.  M. 
B.  H.  P. 

7700 
163 
903 

10850 
231 
2.55 

13300 
283 
4  69 

15400 
326 

7  24 

17170 
365 
10  1 

18800 
400 
13  3 

20300 
432 
16  .7 

21700 
462. 
204 

24250 
516 
28.5 

26600 
566 
37.5 

t 

4* 

CU.  FT 
R.P.M. 
B.  H.  P. 

10000 
143 
1.18 

14150 
202 
3.32 

17350 
248 
6.10 

20000 
286 
9.40 

22400 
320 
13  1 

24500 
1?1 

26500 
378 
21.75 

21WOO 
403 
26.6 

31600 
452 
37.1 

34700 
495 

48.8 

1 

54 

CU.FT. 
R.P.  M. 
B.  H.  P. 

12700 
127 
1  49 

17950 
179 
4  20 

22000 
220 
7  75 

25400 
254 
11.9 

28400 
284 
16  6 

31100 
311 
21.9 

33600 
336 
27  6 

35900 
359 
33.7 

40200 
402 
47.1 

44000 
440 
62 

II 

M 

CU.FT. 
R.P.M. 
B.  H.  P. 

1.VJ50 

114 
1  84 

22100 
161 
5  20 

27100 

.3 

31300 
228 
14  7 

35000 
2S5 
206 

38400 
280 

27.0 

41400 
302 
34.1 

44200 
322 
41  6 

49400 
361 

58.2 

54200 
396 
76  5 

" 

M 

CU.  FT. 
R.P.M. 
B.  H.  P. 

18950 
104 
2  23 

2*00 
6  30 

32850 
180 
11  6 

«jS» 

17.8 

42300 
232 
24.9 

46400 
254 
32.7 

50100 
275 
41  2 

53600 
294 
504 

WJUOU 
328 
704 

65700 
360 
92.6 

12 

72 

CU.FT. 
R.P.  M. 
B.  H.  P. 

22600 
95 
2  66 

31800 
134 
748 

39000 
165 
137 

45200 
190 
21  2 

50000 
212 
296 

55200 
233 
389 

59600 
252 
490 

63600 
269 
59  8 

71200 
301 
836 

78000 
330 
110 

13 

78 

CU.  FT. 
R.P.  M. 
B.  H.  P. 

26400 
88 
3  10 

37350 
124 
8.77 

45800 
153 
16  1 

52800 
176 
24  8 

59100 
197 
34  7 

64700 
215 
45  6 

70000 
233 
57.5 

74700 
248 
70  2 

83500 
278 
98 

91600 
305 
129 

14 

M 

CU.FT. 
R.P.  M. 
B.  H.  P. 

30800 
81 
361 

43400 
115 
10.2 

53200 
142 
18  7 

GI600 
163 

28  9 

68700 
182 
40  4 

75200 
200 
53  0 

81200 
216 
66  8 

86800 
231 
81.7 

97100 
258 
114 

106400 
283 
1.50 

IS 

90 

CU.FT. 

£•£* 

35250 
76 
4.14 

49800 
107 
11.7 

61000 
132 
21.5 

70500 
152 
33.1 

78800 
170 
46.2 

86400 
186 
607 

93300 
201 
76.7 

99600 
214 
93.6 

111200 
24.1 
131 

122000 
264 
172 

171 


Notes         on          Heating         and         Ventilation 

driven  at  so  slow  a  speed  that  it  will  not  produce  suf- 
ficient pressure  to  overcome  resistance  of  the  air  flues. 
Choose  the  largest  fan  that,  driven  at  sufficient  speed 
to  overcome  the  resistance  of  the  air  flue,  will  deliver 
a  proper  quantity  of  air  for  the  purpose  of  ventilation. 
As  an  example :  Suppose  we  wish  to  deliver  to  a  build- 
ing 10,000  cubic  feet  of  air  per  minute.  Referring  to 
the  table,  we  see  that  we  may  use  an  80-inch  fan  driven 
at  400  revolutions,  in  which  case  there  would  be  re- 
quired 5  horsepower  to  drive  the  fan  and  the  pressure 
produced  would  be  .713  ounce  or  we  might  use  a 
120-inch  fan  driven  at  125  revolutions  per  minute, 
in  which  case  the  power  required  to  drive  the  fan 
would  be  2.9  horsepowers  and  the  pressure  produced 
would  be  .153.  In  the  first  case  the  fan  is  small  and 
being  driven  at  high  speed  the  pressure  produced  is 
more  than  necessary  to  overcome  the  resistance  required 
except  when  the  flues  are  long  and  have  a  number  of 
turns.  In  the  case  of  the  120-inch  fan,  while  the  horse- 
power is  much  lower  the  pressure  is  insufficient  to  over- 
come the  ordinary  resistance.  For  ordinary  purposes 
the  pressure  should  be  about  .25-.50.  Referring  again 
to  the  table,  we  see  that  the  100-inch  fan  driven  at  200 
revolutions  per  minute  would  require  3.15  horsepowers 
and  produce  a  pressure  of  .274.  This  would  be  about 
the  proper  size  of  fan  for  most  cases.  The  pressure 
required  to  overcome  the  resistance  of  the  building  de- 
pends very  largely  upon  the  capacity  and  design  of  the 
flues  and  the  resistance  of  these  flues  is  largely  a  mat- 
ter of  judgment  and  experience. 

Heating    Coils. — The    determination   of   the   proper 
quantity  of  heating  coil  to  raise  the  air  to  a  given  tem- 

172 


Notes 


o  n 


Heating         and         Ventilation 


Table  XLVIII—  Condensation  and  Heat  Given  Off  by 

Heater  Coils. 

TEMPERATURE  AIR  ENTERING  COIL  0°-10° 

i 

Velocity  of  Air 
1000  feet  per 

Velocity  of  Air 
1250  feet  per 

Velocity  of  Air 
1500  feet  per 

Velocity  of  Air 
1700  feet  per 

• 

minute. 

minute. 

minute. 

minute. 

.2 

8 

8 

§§    - 

g  o 

C  o 

2° 

00 

00-3 

00 

£8 

1 

ondensatl 
r  square  f 
n  pounds 

emperatu 
leaving 
degrees. 

ondensati 
r  square  f 
n  pounds 

emperatu 
leaving 
degrees. 

ondensati 
-  square  f 
n  pounds 

emperatu 
leaving 
degrees. 

sndensati 
-  square  f 
n  pounds 

5  hew 

1 

£ 

a 

H-s 

°S 

H'S 

°a 

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°£ 

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4 

i 

2.90 

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2.4 

35 

2.68 

32 

2.85 

31 

8 

2 

1.92 

74 

2.21 

65 

2.46 

60 

2.65 

55 

12 

3 

1.78 

94 

2.1 

82 

2.32 

77 

2.45 

73 

16 

4 

1.53 

114 

1.86 

98 

2.09 

93 

2.25 

88 

20 

5 

1.31 

130 

1.68 

115 

1.88 

108 

2.10 

103 

24 

6 

1.20 

143 

1.54 

128 

1.77 

122 

1.92 

117 

28 

7 

1.10 

152 

1.45 

140 

1.70 

134 

1.85 

129 

32 

8 

1.05 

1.40 

148 

1.65 

140 

1.77 

133 

TEMPERATURE  AIR  ENTERING  COIL  40°-50° 

1 

d 

Velocity  of  Air 
1000  feet  per 

Velocity  of  Air 
1^50  feet  per 

Velocity  of  Air 
1500  feet  per 

Velocity  of  Air 
1700  feet  per 

.2 

r 

minute. 

minute. 

minute. 

minute. 

'§ 

CO 

c 
o 

c  o 

2° 

C  0 

s£d 

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gl  . 

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ondensat 
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•  leaving 
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ondensat 
r  square 
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0>~ 

ondensat 
r  square 
in  pound 

emperatl 
square  f 
degrees. 

ondensat 
r  square 
in  pound 

oT>  2 

°a 

H'S 

O  <u 

a 

H'3 

°a 

a 

O  4> 

a 

H-3 

8 

2 

1.75 

91 

2.07 

84 

2.37 

80 

2.52 

78 

12 

3 

1.50 

107 

1.80 

100 

2.06 

95 

2.23 

93 

16 

4 

1.41 

119 

1.65 

112 

1.89 

107 

2.02 

105 

20 

5 

1.37 

133 

1.60 

125 

1.80 

121 

1.90 

119 

24 

6 

132 

143 

1.50 

137 

1.67 

135 

1.77 

133 

28 

7 

1.26 

150 

1.40 

145 

1.56 

142 

1.64 

140 

32 

8 

1.14 

158 

1.30 

252 

1.48 

148 

1.52 

147 

173 


Notes 


on          Heating          and          Ventilation 


perature  will  depend  primarily  upon  the  amount  of  heat 
given  off  per  square  foot  of  heater  coil. 

Table  XLVIII  is  obtained  from  the  results  of  experi- 
ments made  by  the  American  Blower  Company,  of  De- 
troit, and  shows  the  condensation  and  heat  given  off  by 
ordinary  pipe  heater  coils  under  different  conditions. 
Knowing  the  heat  given  off  by  the  coil  per  square  foot, 
under  given  conditions,  the  number  of  square  feet  of 
coil  surface  necessary  may  be  obtained  in  the  following 


manner:  Multiply  the  air  to  be  passed  per  hour  by  the 
difference  between  the  temperature  of  the  outside  air 
and  the  temperature  of  the  air  after  passing  through 
the  coil.  Multiply  this  product  by  .2375.  Divide  the 
result  obtained  by  13.3,  multiplied  by  the  condensation 
per  square  foot  of  surface  per  hour,  multiplied  by  966. 
Let  C  =  condensation  per  square  foot  of  coil ;  V  =  vol- 
ume of  air  in  cubic  feet  passing  per  hour ;  F  =  square 
feet  heating  surface  coil  should  contain ;  t  =  tempera- 
ture outside  air ;  V  =  temperature  of  air  after  passing 
coil ;  then 

.2375V(t'— t) 
F  = 

13.3  X  966  C 

174 


Notes 


o  n 


Heating          and          Ventilation 


After  determining  the  number  of  square  feet  of  sur- 
face in  the  heater  the  heater  must  be  so  designed  as  to 
allow  sufficient  air  area  for  the  passage  of  air  through 
the  heater  coils.  The  coils  as  ordinarily  arranged  are 
shown  in  Fig.  62.  Sufficient  area  should  be  allowed  in 
these  coils  for  the  velocity  of  air  passing.  This  should 
not  exceed  1,200  feet  per  minute,  except  where  coils  are 


very  large.  Tempering  coils  should  not  be  less  than  12 
pipes  deep.  If  the  tempering  coils  are  made  very  shallow 
the  condensation  in  the  coil  is  so  rapid  that  in  cold 
weather  they  will  hammer. 

The  heater  coil  consists  of  a  cast  iron  base  into  which 
is  screwed  1-inch  steam  pipes  jointed  at  the  top  by 
nipples  and  elbows.  The  cast  iron  base  for  each  section 
is  provided  with  a  steam  inlet  and  drip,  both  connected 
to  the  cast  iron  heater  base.  Most  bases  are  constructed 

175 


Notes         on          Heating         and         Ventilation 

for  four  rows  of  pipes.  Table  XLIX  gives  the  principal 
dimensions  of  the  American  Blower  Company's  heaters 
with  the  size  of  fan  regularly  used. 

Cast  Iron  Heaters. — Within  the  last  few  years  cast 
iron  indirect  radiators  suitable  for  use  with  fans  have 
been  placed  on  the  market.  Figure  63  shows  a  group  of 
ten  of  these  sections.  They  are  easier  to  handle  in  erec- 
tion and  less  liable  to  rust.  The  standard  sizes  on  the 
market  are  41  and  60^  inches  in  length ;  both  sizes  are 
9%  inches  deep  and  each  section  takes  up  a  width  of 
5  inches.  The  60-inch  section  contains  17  square  feet 
per  section  and  the  40-inch  section  Iiy2  square  feet. 
The  table  sections  are  tapped  2^  inches  and  may 

TABLE  XLIX.— HEATER  DIMENSIONS. 

Lineal  feet  Net  air  Size  of  fan. 

capacity  of           — -Connections. —  space  in  Regular  Steel 

1-inch  pipe.  Steam.  Drip.  Bleeder.  sq.ft.  Disc.  Plate. 

200  2     "  1     "  ~:    %"  5.4  30  80 

300  2     "  1     "  M"  7.6  36  90 

400  2     "  1%"  '%"  10.7  42  100 

525  -'     "  1%"  1     "  14.3  48  110 

650  2     "  1%"  1     "  17.7  54  120 

825  2%"  1%""  1     "  22.2  60  140 

1,175  2%"  1%"  1     "  31.  72  160 

1,525  3     "  2     "  1*4"  40.  84  180 

2,025  3     "  2     "  11A"  52.5  96  200 

be  bushed  to  the  proper  size,  depending  on  the 
number  of  sections  composing  the  radiator.  Fig.  64 
shows  a  curve  of  the  steam  condensation  for  these  ra- 
diators with  varying  depth  of  coil  and  different  veloci- 
ties of  air.  Figure  65  shows  the  temperature  to  which 
the  air  would  be  heated  in  passing  through  these  coils 
with  varying  depth  of  coil  and  different  velocities  of 
air.  The  last  two  cuts  are  from  the  results  given  by 
the  American  Radiator  Co. 

176 


Notes 


on 


Heating         and         Ventilation 


Ventilating  Ducts. — The  success  of  the  fan  system 
depends  very  largely  upon  the  design  of  the  flues.     The 

Condensation  Chart 

Incoming  air,  o°  Fahrenheit.     Steam  pressure,  5  pounds 


1.10 
1.15 
1  20 
1  25 
1  30 

1.40 
1.45 
1.50 
1  55 
1  60 

1  70 
1  75 

1  85 
1  90 
1  95 
2  00 
2  05 
2  10 
2  15 
2  20 
2.25 
2.30 
2  35 
2  40 

2  50 
2  55 
2.60 
2  65 
2.70 
2.75 
2  80 

1072 
1121 

V 

\ 

\ 

s 

1219 
1267 
1316 
1365 
1414 
1462 
1511 
1560 
1608 
1657 
1706 

1804 
1852 
1901 
1950 
1999 
2047 
2096 
2145 
2194 
2242 
2291 
2340 
2389 
2437 
2486 
2535 
2584 
2632 
2681 
2730 

V 

S 

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500      600      700-800      900     1000    1100    1200    1300     1400    1500 
Velocity  of  Air  Through  Heater  in  Feet  per  Minute 

Fig.    64. 


best  form  of  flue  is  round,  the  next  best  form  is  square, 
or,    if    rectangular,    is    nearly   square    as    possible.      All 


17T 


Notes         on         Heating         and         Ventilation 

turns  and  branches  should  be  made  with  easy  curves. 
The  size  of  the  flues  is  ordinarily  determined  by  the 
velocity  of  the  air  passing  in  the  flues.  In  main  ducts 
of  large  size  a  velocity  as  high  as  1,500  feet  per  minute 
may-  be  used.  In  the  branch  main  or  small  main  duct? 


Temperature  Chart 

Initial  air  temperature.  o°  Fahrenheit.      Steam  pressure, 
220.c 


pounds 


500.     600       700 


900-    1000.    1100.    1200.   1300     1400.    1500. 


Velocity  of  Air  Through  Heater  in  Feet  per  Minute. 
Fig.   65. 

the  velocity  should  not  exceed  800  to  1,000  feet.  In 
flues  leading  to  the  individual  rooms  the  velocity  should 
be  from  600  to  800  feet  per  minute,  depending  upon 
their  size.  Where  the  ducts  are  of  small  size  this  ve- 
locity is  often  reduced  to  400  feet  per  minute.  The 

178 


Notes         on         Heating         and         Ventilation 

velocity  at  the  registers  should  not  exceed  300  feet  per 
minute  except  in  very  large  registers  so  located  that  the 
current  of  air  entering  the  room  will  not  strike  the  occu- 
pants of  the  room,  then  the  velocity  may  be  500  feet 
per  minute.  In  all  ordinary  buildings,  if  these  propor- 
tions of  air  velocities  are  used  the  resistance  of  the  sys- 
tem will  be  from  .3  to  .6  of  an  ounce  pressure.  The 
loss  of  pressure  in  a  piping  system  of  square  or  round 
pipe  may  be  determined  from  the  following  expression 
used  by  the  U.  S.  Navy  Department  : 

1 
Hf  =  4f  —  Vi2 

d 

Where  H  is  the  loss  of  pressure  due  to  friction  meas- 
ured in  head  of  air  in  feet,  f  is  the  coefficient  of  fric- 
tion, 1  and  d  are  length  and  diameter  of  pipe,  both  in 
feet  or  both  in  inches,  and  V^  is  the  velocity  of  flow 
through  the  pipe  in  feet  per  second.  If  V±  is  changed 
to  V,  or  velocity  in  feet  per  minute,  and  f  given  its 
proper  value,  which  for  good  piping  is  .00008,  then 

1  V2 


d     11,250,000 

1 

If  V  =  2,000,  Hf  =  .3556  — 

d 

1 

If  V  =  1,000,  Hf  =  .0889  - 

d 

For  rectangular  pipe  of  short  side  h  and  long  side  nh 
the  formula  becomes  : 

1  +  n      1          V2 


n         h    2,250,000 
179 


Notes         on          Heating         and         Ventilation 

Where  1  =  length  of  pipe  and  V  is  velocity  of  air 
through  it  in  feet  per  minute.  If  a  standard  pressure  be 
assumed  of  5  pounds  per  square  foot,  which  corresponds 
to  a  head  of  air  of  84.25  ft.,  then  for  each  foot  of  head 
lost  there  will  be  a  loss  in  delivery  of  .6  or  1  per  cent. 
For  example,  suppose  364  feet  per  minute  are  required 
at  a  given  outlet,  where  the  total  head  is  69.67,  a  loss  of 
15  feet.  The  corresponding  loss  of  delivery  would  be 
9  per  cent  and  the  rated  capacity  of  the  pipe  to  delivery 
of  this  air  should  be  364/91  =  400  cubic  feet  per  minute. 
In  determining  the  length  of  a  pipe  a  90°  elbow  is 
equal  to  5  diameters  of  pipe  provided  the  radius  to  the 
center  of  the  pipe  is  not  less  than  \y2  diameters.  A 
smaller  radius  than  this  should  not  be  used,  as  it  in- 
creases the  resistance  very  rapidly.  Where  branches 
leave  the  main  ducts  it  is  a  common  practice  to  place 
a  deflecting  damper  at  the  bend  of  the  branch.  This  is 
merely  a  piece  of  galvanized  iron  attached  to  the  point 
of  the  branch,  which  may  be  adjusted  and  fastened  so 
that  each  branch  will  take  its  proper  supply  of  air. 
Dampers  controlled  by  the  attendants  in  the  building 
should  be  as  few  as  possible.  The  reductions  in  the  size 
of  a  flue  should  be  made  gradually.  The  angle  of  the 
reduction  should  not  exceed  a  taper  of  \l/2"  per  foot. 
No  round  pipes  less  than  6  inches  in  diameter  are  used, 
and  if  rectangular,  less  than  6x8.  A  common  arrange- 
ment of  ducts  is  to  let  them  radiate  from  the  fan  in  the 
form  of  a  tree,  with  trunk  and  branches.  Another  very 
satisfactory  method  of  distribution  is  to  force  all  the 
air  from  the  fan  into  a  large  duct  or  chamber  in  which 
the  air  has  a  very  low  velocity. 

180 


Notes          on          Heating         and         Ventilation 

The  rooms  take  their  air  from  this  chamber  by  means 
of  vertical  flues  controlled  by  proper  dampers.  These 
large  chambers  are  called  Plenum  chambers.  A  good 

TABLE  L.— PRESSURE  LOSSES. 

Air. — Loss  of  Pressure  in  Ounces  per  S'quare  Inch  per  100  Feet  of 
of  Pipe  of  Varying  Velocities  and  Varying  Diameters  of  Pipes. 


Velocity  ol  Aft 
Feet  per 
Minute. 

DIAMETER  OF  PIPE  IN  INCHES. 

1 

Loss  or  PRESSURE  IN  OUNCES. 

600 

[JS 

a 

3600 
4,200 
4800 

eiooo 

.400 

1.600 
8.600 
6.400 
10.000 
14/400 

.200 

.800 
1.800 
8.200 
5.000 
7.200 
9.800 
12.800 
20.000 

133 
.533 
1.200 
2.133 
3.333 
4.800 
6553 
8.533 
13.333 

.100 
.400 

2^500 
8.600 
4.900 
6.400 
10.000 

.060 
.820 
.720 
1.280 
2.000 
2.880 
3.920 
5.120 
8.000 

3? 

.600 
1.067 
1.667 
2.400 

!:£ 

6.667 

Ml 
.228 
.514 
.914 

2^800 
8.657 
B.714 

.050 

3 

.800 
1.250 
1.800 
2.450 
8200 
i.000 

Velocity  o(  Air 
Feet  per 
Minute. 

DIAMETER  OF  PIPE  IN  INCHES 

9 

10 

11 

12 

14 

16 

18 

20 

Loss  OP  PRESSURE  IN  OUNCES. 

600 
1,200 

1800 

8000 

4/200 
4.800 
6,000 

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I 

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1.111 

1.600 
2.178 
2.844 
4  444 

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.160 
.860 
.640 

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1.960 

3£g 

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.woi 

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iS 

Velocity  of  Air 
Feet  per 
Minute. 

DIAMETER  OF  PIPE  IN  INCHES. 

22 

24 

28 

32 

36 

40 

44 

48 

Loss  or  PRESSURE  IN  OUNCES. 

600 

I'm 

£& 

eiooo 

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.073 

3 

.655 
.891 
1.164 

1.818 

.017 
.067 

g 

.600 
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-1.067 
1.667 

.014 

.057 

!514 
.700 
.914 
1.429 

.012 
.050 

i8 

.450 
.612 
.800 
1.250 

.011 
.044 
.100 

.544 
.711 
1.111 

.010 
.040 
.090 

:490 
.640 

1.000 

.009 
.036 
.082 
.•145 
.827 

i 

.006 

fi 

.138 
.800 
.408 
.533 

.888 

example  of  this  is  shown  in  the  construction  of  the  new 
Engineering  building,  University  of  Michigan.  In  this 
building  the  corridor  on  the  ground  floor  has  a  false 


181 


Notes 


o  n 


Heating          and          Ventilation 


ceiling  about  3  feet  below  the  second  story  floor.  This 
leaves  a  space  3  feet  high  by  12  feet  wide  extending 
through  the  entire  building.  Into  this  space  two  separate 
fans  deliver  their  air.  The  -space  acts  as  a  Plenum 
chamber  and  the  individual  flues  leaving  the  rooms  take 
their  air  from  this  Plenum  chamber  through  volume 
dampers  which  may  be  set  and  fastened  after  the  proper 
position  has  once  been  determined. 

Table  L  shows  the  loss  of  pressure  per  100  feet  of 
pipe  for  varying  velocities  and  -varying  diameters  of 
pipes.  This  table  is  quite  liberal  and  allows  for  two 
ordinary  90°  bends  per  100  feet. 

Air  Mixing  Systems. — Where  the  building  is  heated 
entirely  by  a  fan  system  it  is  necessary  to  devise  some 
arrangement  by  which  the  room  may  be  furnished  with 


Fig.   66. 

hot  air  or  tempered  air.  In  case  the  room  becomes  too 
warm,  to  close  off  the  hot  air  register  would  do  away 
entirely  with  ventilation  and  it  is  necessary  to  provide 
some  means  of  introducing  tempered  air.  The  method 
usually  is  shown  in  Fig.  62.  Where  each  room  is  con- 
nected both  to  the  warm  air  chamber  and  to  the  cold  air 
passage,  the  dampers  being  connected  so  that  when  the 
warm  air  is  turned  off  cold  air  is  introduced  into  the 
room,  or  vice  versa.  In  this  case  the  mixing  damper  is 

182 


Notes          on         Heating 


and 


Ventilation 


located  near  the  fan  and  preferably  controlled  automat- 
ically. Another  system  shown  in  Fig.  66  has  entirely 
separate  cold  and  hot  air  flues  which  are  led  to  the  base 

TABLE  LI.— DISC   FAN  EFFICIENCY. 


Dies  Ventilating  Fan  —  Capacity,  Speeds  and  Horse  Powers   (Amer- 
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of  vertical  flues  leading  to  the  rooms,  at  which  point 
there  is  introduced  a  mixing  damper  similar  to  the  mix- 
ing damper  shown  in  Fig.  62. 

183 


Notes          on          Heating          and          Ventilation 

Materials  of  Flues. — The  flues  for  fan  systems  are 
ordinarily  constructed  of  galvanized  iron  with  double 
lap  joints  riveted  or  soldered.  The  ducts  should  be  made 
as  nearly  as  possible  air-tight.  The  weight  of  material 
used  for  ducts  depends  upon  the  size  of  the  duct.  It 
ordinarily  varies  from  No.  26  to  No.  20  gauge.  Large 
ducts  are  also  made  of  sheet  iron  with  close  riveting. 
When  ducts  are  made  of  sheet  iron  the  ducts  are  painted 
and  then  asphalted.  Where  it  is  necessary  to  build  ducts 
underground  they  are  built  of  brick  or  cement.  The  ce- 
ment, if  anything,  is  preferable  to  brick,  as  it  does  not 
absorb  odors  as  easily  and  may  be  plastered  to  make  a 
e-mooth  job.  Where  possible  it  is  desirable  to  build  the 
ducts  and  flues  into  the  building  itself,  making  them  of 
permanent  material.  Brick  or  cement  ducts  built  into 
the  building  and  so  arranged  that  they  may  be  examined 
and  cleaned  easily  are  the  most  satisfactory.  Wood  is 
always  a  bad  material  to  use  for  ducts  and  should  be 
avoided.  Where  it  is  used  the  ducts  are  lined  with  tin, 
owing  to  the  fact  that  wood  usually  shrinks,  leaving 
open  joints. 

Vent  ducts  from  closets  should  be  carried  out  of  the 
buildings  separately  from  the  other  vent  flues.  Where 
these  ducts  are  made  of  brick  they  should  be  lined  with 
galvanized  iron  to  prevent  the  odors  from  the  closet  be- 
ing absorbed  by  the  brick.  It  is  very  desirable  that 
closet  vents  should  be  collected  at  convenient  points  and 
then  exhausted  from  the  building  by  means  of  a  fan. 
This  prevents  the  odors  from  the  toilet  rooms  being  car- 
ried back  into  the  building. 

Disc  Fans. — Disc  fans  are  used  where  the  resistance 
to  be  overcome  is  very  slight  or  in  cases  where  the  ducts 

184 


Notes          on          Heating          and          Ventilation 

are  very  large,  with  easy  turns  and  of  very  short  length. 
They  are  extensively  used  for  exhausting  the  air  from 
the  vent  flues  and  where  the  vent  flues  are  short  and 
large  they  give  good  satisfaction.  The  capacity,  speed 
and  horsepower  of  various  sizes  of  disc  fans  is  shown, 
in  Table  LI. 

EXAMPLE. — As  an  example  of  the  fan  system  consider 
an  auditorium.  The  dimensions  of  the  room  are  40  feet 
9  inches  by  79  feet  G  inches  by  127  feet  9  inches.  The 
volume  of  the  room  is  413,000  cubic  feet.  It  has  203 
square  feet  of  glass  surface  and  5,441  square  feet  of  wall 
surface.  The  heat  lost  from  the  room,  figuring  in  the 
same  way  as  we  have  for  previous  examples,  will  be 
168,010  B.  T.  U.'s.  The  hall  has  a  seating  capacity  of 
2,500  persons.  Allowing  2,000  cubic  feet  of  air  per  per- 
son, the  necessary  air  to  be  admitted  to  the  room  will 
be  5,000,000  cubic  feet  of  air  per  hour.  This  equals  383,- 
000  pounds.  In  order  to  heat  the  room  with  this  quan- 
tity of  air  entering,  it  will  be  necessary  to  heat  the  air 
but  1.85  degrees  so  that  the  air  admitted  to  the  room 
for  ventilating  purposes  will  be  far  more  than  that  nec- 
essary for  heating  purposes.  It  is  best,  then,  to  figure 
on  admitting  air  only  for  purposes  of  ventilation.  To 
heat  this  air  from  zero  to  70°  would  require  383,000 X 
.2375X70=6,353,000  B.  T.  U.'s.  Referring  to  Table 
XLV,  we  see  that  a  heater  coil  12  pipes  deep  will  heat 
air  having  a  velocity  of  1,250  feet  per  minute  to  a  tem- 
perature of  82°,  which  is  probably  about  the  proper 
assumption  to  make  in  this  case.  The  coil  will  condense 
2.1  pounds  of  steam  per  square  foot  per  hour.  Each 
pound  gives  up  about  970  heat  units,  so  that  each  square 
foot  of  heater  coil  will  give  off  about  2,000  B.  T.  U.'s 
per  hour.  Then  the  number  of  square  feet  of  heater  coil 
required  would  be  6,350,000-^2,000=3,175  square  feet. 

185 


Notes         on          Heating         and         Ventilation 

The  heater  coils  are  usually  made  of  1-inch  pipe  and 
each  square  foot  of  surface  is  equivalent  to  about  3  feet 
of  1-inch  heater  pipe,  hence  there  will  be  required  3,175 
X3  or  9,525  feet  of  1-inch  pipe  in  the  heater  coils.  The 
air  to  be  admitted  to  the  hall  is  5,000,000  cubic  feet  per 
hour  or  83,300  cubic  feet  per  minute.  The  usual  velocity 
allowed  for  the  air  passing  through  the  heater  coil  is 
1,200  feet  per  minute.  This  will  require  an  air  area  in 
the  heater  coil  of  83,000-^1,200=69.5  square  feet.  The 
area  in  the  various  heater  coils  will  be  found  in  the 
blower  company's  catalogues  and  is  also  given  in  Table 
XLVIII.  This  will  determine  the  size  of  the  heater  coil 
to  be  used. 

On  account  of  the  size  of  the  hall  and  the  amount  of 
air  introduced,  it  will  be  best  to  have  two  fans  for  deliv- 
ering air  into  the  building.  Each  fan  would  then  need 
a  capacity  of  41,650  cubic  feet  per  minute.  In  order  to 
overcome  the  resistance  of  the  flues  the  pressure  should 
be  from  A  to  .5  of  an  ounce  at  least.  From  the  table 
of  fan  capacities  we  see  that  a  180-inch  fan  running  at 
150  revolutions  would  require  19.6  horsepowers  and  pro- 
duce a  pressure  of  .503  ounces  and  give  the  air  required. 
Assuming  the  air  to  be  delivered  to  the  hall  by  four 
ducts,  these  ducts  being  large,  it  would  be  reasonable  to 
allow  a  velocity  of  1,000  feet  per  minute  in  the  duct. 
Each  duct  would  have  to  carry  20,800  cubic  feet  of  air 
per  minute;  20,800^-1,000=20.8  square  feet  in  area.  As 
the  registers  of  these  ducts  will  be  large  and  situated 
well  above  the  head  line,  it  would  be  safe  to  allow  a 
velocity  of  400  feet  per  minute  through  the  register.  The 
area  of  each  register,  assuming  that  there  are  four  en- 
tering the  room,  would  be  26  square  feet.  The  vent 
flues  leaving  the  room  should  have  an  area  about  equal 
to  the  hot  air  flues. 

186 


CHAPTER  XII. 

A  CENTRAL  HEATING  SYSTEM. 

Design  and  Location. — It  is  not  intended  in  this 
chapter  to  discuss  the  design  of  heating  systems,  such 
as  is  used  in  the  heating  of  a  city,  but  systems  that 
are  in  use  for  the  heating  of  public  institutions,  or 
groups  of  buildings.  The  type  of  system  to  be  used 
in  a  given  installation  depends  very  largely  upon  the 
location  and  character  of  the  building  to  be  heated. 
No  two  systems,  even  though  designed  by  the  same 
engineer,  will  be  the  same,  and  the  suggestions  made 
in  this  chapter  can  be  but  general. 

Before  starting  the  design  of  a  general  heating  sys- 
tem it  is  first  necessary  to  have  a  careful  survey  of 
the  property.  This  survey  should  show  the  exact 
location  of  the  buildings  to  be  heated,  the  elevation 
of  the  basement  and  first  floor,  together  with  a  gen- 
eral profile  of  the  ground  through  which  the  tunnels 
or  pipes  are  to  be  run.  The  profile  of  the  ground  will 
largely  decide  the  proper  location  of  the  power  house. 
The  power  house  should  be  located  as  nearly  as 
possible  to  the  buildings  to  be  heated  or  as  near  as 
possible  to  the  largest  steam  load.  It  should  be  low 
enough,  if  the  profile  of  the  land  will  permit,  so  that 
the  condensation  of  the  return  mains  may  be  returned 
to  the  power  house  by  gravity.  If  possible,  it  should 
be  so  located  that  the  floor  of  the  boiler  room  may 
be  drained  to  the  sewer.  Considerable  difficulty  is  usu- 
ally experienced  to  carry  away  the  water,  which  re- 
sults from  the  cleaning  and  blowing  off  of  the  boilers 

187 


Notes         on          Heating         and         Ventilation 

if  no  sewer  connection  can  be  made.  The  question  of 
the  soil,  the  location  of  the  railroad  siding,  the  water 
supply  and  the  general  appearance  of  the  power  house 
must  also  be  taken  into  consideration. 

Boilers. — Before  designing  the  power  house  the 
type  and  general  form  of  boilers  must  be  determined. 
If  the  power  house  is  to  work  on  a  low  pressure  system 
with  a  pressure  under  100  pounds,  either  fire  or  water 
tube  boilers  may  be  used.  In  general,  for  this  service 
fire  tube  boilers  are  very  satisfactory,  as  they  have 
large  water  storage,  repairs  are  easily  made,  and  the 
boiler  may  be  crowded  considerably  beyond  its  rating. 
The  economy  of  water  tube  and  fire  tube  boilers  is  prac- 
tically the  same. 

The  principal  objection  to  fire  tube  boilers,  except  of 
the  Scotch  marine  type,  is  the  large  space  which  it  oc- 
cupies. If  the  power  house  is  to  be  operated  on  high 
pressure,  that  is,  over  100  or  125  pounds,  then  only 
water  tube  or  Scotch  marine  boilers  can  be  used.  The 
size  of  the  boiler  must  be  determined  by  the  amount 
of  steam  which  is  to  be  used  by  the  radiation  and  other 
devices  taking  steam  from  the  boilers.  The  steam  used 
by  the  different  forms  of  radiation  can  be  determined 
by  reference  to  the  radiator  tables  previously  given, 
and  to  ihis  must  be  added  the  steam  used  by  auxiliaries, 
by  the  kitchen,  the  condensation  in  the  main  and  all 
other  devices  using  steam.  After  having  once  de- 
termined the  quantity  of  steam  the  plant  is  expected 
to  use,  it  is  customary  to  assume  that  each 
square  foot  of  heating  surface  in  a  boiler  will 
evaporate  about  three  pounds  of  water.  This  deter- 
mines the  total  -imount  of  heating  surface  that  the 

188 


Notes          on          Heating          and          Ventilation 

boilers  should  contain.  The  boiler  units  should  be  so 
selected  that  one  boiler  or  one  set  of  boilers  will  take 
care  of  the  plant  during  the  light  load  period  of  opera- 
tion, that  two  boilers  or  sets  of  boilers  will  take  care  of 
the  average  operating  load.  In  addition  to  this  there 
should  be  a  boiler  or  set  of  boilers  that  will  take  care 
of  the  maximum  conditions  of  load.  There  should  al- 
ways be  a  sufficient  number  of  boilers  in  the  plant  so  that 
at  least  one  boiler  or  set  of  boilers  can  be  out  of  service 
for  a  considerable  period  of  time  for  cleaning  or  re- 
pairing. In  a  central  heating  plant  using  the  gravity 
return  system,  it  is  necessary  that  all  boilers  have  their 
water  line  at  the  same  level. 

Systems  of  Distribution. 

The  general  design  of  a  piping  system  and  its  lo- 
cation will  depend  upon  the  system  of  distribution 
adopted. 

Gravity  System. — If  the  gravity  return  system  is 
used  no  main  feed  pump  is  necessary,  the  water  re- 
turning by  gravity  to  the  boiler,  as  previously  described. 
With  this  system  any  difference  in  pressure  between 
that  in  the  boiler  and  that  at  the  extreme  point  in  the 
piping  system  will  result  in  a  corresponding  elevation 
of  the  water  level  in  the  return  system  at  the  extreme 
point — each  one  pound  drop  of  pressure  in  the  steam 
piping  corresponds  to  an  increase  in  the  level  of  the 
water  in  the  return  piping  of  2.30  feet.  It  is  essential, 
then,  that  with  a  gravity  return  system  the  difference  in 
pressure  between  the  boiler  and  the  extreme  point  of 
the  piping  system  be  comparatively  small. 

The   difference  of   pressure  assumed  will   determine 

189 


Notes         on         Heating         and         Ventilation 

the  size  of  the  piping.  In  gravity  systems  it  is  usual 
to  allow  for  the  drop  of  pressure  not  over  two  pounds 
between  the  boiler  and  the  extreme  end  of  the  system. 

In  some  cases  the  gravity  return  system  has  been 
used  Over  quite  an  extended  area,  the  most  distant  build- 
ing heated  being  as  far  as  2,500  feet  from  the  boiler,  and 
the  system  has  given  very  good  satisfaction. 

In  a  central  heating  plant  using  the  gravity  return 
system  unless  the  steam  mains  are  six  to  eight  feet  above 
the  return  it  is  necessary  that  the  steam  condensed  in 
the  mains  be  dripped  separately  from  the  main  re- 
turns in  the  building  and  this  drip  pumped  back  to  the 
boilers,  preferably  by  a  pump  and  receiver,  or  some 
other  mechanical  means,  such  as  a  return  trap.  This 
pump  and  receiver  should  be  of  sufficient  size  to  take 
care  of  the  steam  condensed  in  the  mains  when  the 
steam  is  being  turned  on  and  the  condensation  is  ex- 
cessive. By  returning  the  condensation  of  the  mains 
separately,  excessive  hammering  is  avoided  and  the  sys- 
tem can  be  started  much  more  rapidly.  Gravity  return 
is  used  only  where  the  boiler  pressure  does  not  exceed 
ten  pounds. 

High  Pressure  System. — The  high  pressure  steam 
is  sometimes  used  for  general  heating  purposes,  but  the 
pressure  is  reduced  through  a  reducing  valve  before  en- 
tering the  radiators.  It  has  some  advantages.  The 
pipes  are  smaller  and  circulation  is  very  rapid  in  this 
system.  It  is  not  possible  to  use  exhaust  steam  with  a 
high  pressure  system.  When  pipe  coil  radiation  is  used 
it  would  be  safe  to  carry  a  pressure  up  to  100  pounds  on 
the  radiators,  but  high  pressure  in  the  radiators  is  not 
good  practice.  In  determining  the  size  of  steam  mains  for 

190 


Notes         on         Heating         and         Ventilation 

such  a  system  a  loss  of  pressure  as  high  as  ten  pounds 
would  not  be  considered  excessive.  In  the  high  pressure 
system  each  building  usually  sends  its  condensation  back- 
to  the  return  system  through  a  trap  so  that  the  pres- 
sure on  the  return  is  only  slightly  above  the  atmosphere. 
This  condensation  returns  to  a  surge  tank,  from  which 
the  feed  pumps  return  it  back  to  the  boilers.  The  drip 
from  the  steam  mains  is  dripped  directly  back  into  the 
return  system. 

Low  Pressure  Pump  Return  System. — In  a  very 
large  system  where  it  is  difficult  to  get  enough  differ- 
ence in  elevation  between  steam  and  return  mains,  or 
where  the  drop  in  pressure  exceeds  two  pounds,  it  is 
usual  to  install  some  form  of  pump  return.  One  of  the 
most  common  forms  of  pump  return  is  to  trap  the  re- 
turn condensation  of  each  building  into  the  return  main, 
which  carries  the  return  back  to  a  surge  tank  in  the 
boiler  room.  From  this  surge  tank  the  water  is  re- 
turned to  the  boiler  by  means  of  a  pump.  The  drip 
from  the  steam  main  is  trapped  directly  to  the  return 
main.  The  most  objectionable  feature  of  this  system 
is  the  constant  attendance  and  the  repairs  necessary  to 
take  care  of  the  traps. 

Combination   of   Power   and   Heating   System. — In 

most  cases  the  heating  system  is  combined  with  some 
form  of  power  system.  This  makes  a  very  economical 
combination,  as  the  exhaust  from  the  power  plant  may 
be  used  in  the  heating  system.  Where  the  exhaust  can 
be  entirely  utilized  for  from  six  to  eight  months  of  the 
year  it  is  seldom  profitable  to  use  condensing  engines. 

There  are  two  general  schemes  used  for  combining 
a  power  and  heating  system.  In  the  simplest  form  the 

191 


Notes         on         Heating         and         Ventilation 

boilers  are  operated  at  a  high  pressure.  The  steam  goes 
from  the  boilers  to  the  engine,  and  after  the  steam 
leaves  the  engine  it  passes  directly  to  the  heating  sys- 
tem. A  by-pass  pipe  is  carried  from  the  high  pressure 
steam  main  to  the  heating  main  and  in  this  by-pass  is 
located  a  reducing  pressure  valve.  If  for  any  reason 


Fig.    67. 

the  engine  does  not  supply  sufficient  steam  to  maintain 
pressure  on  the  heating  system,  then  the  reducing  valve 
opens  and  introduces  live  steam.  The  returns  from 
the  heating  system  are  carried  back  to  the  boiler  by 
means  of  a  pump. 

Fig.  67  shows  the  general  arrangement  of  systems 
of  this  kind  with  a  by-pass  for  furnishing  live  steam  to 
a  heating  system.  This  system  depends  in  a  measure 
for  its  success  upon  the  action  of  the  reducing  pressure 
valve. 

The    cross-section    of    a    reducing   pressure    valve    is 

192 


Notes 


o  n 


Heating         and         Ventilation 


shown  in  Fig.  G8.  Such  valves  have  been  found  to 
be  quite  reliable  when  well  designed  and  well  made. 
The  principle  cause  for  trouble  is  when  the  valve  be- 
comes foul  with  dirt.  In  a  system  of  this  kind  the  en- 
gine exhaust  is  always  provided  with  a  back  pressure 


Fig.   68. 

valve  connected  to  the  atmosphere.  This  valve  is  so 
arranged  that  if  for  any  reason  excessive  pressure 
should  accumulate  in  the  heating  system  the  valve  would 
open  and  exhaust  the  steam  into  the  atmosphere.  The 
arrangement  shown  in  Fig.  67  is  most  used  in  small 
plants  and  both  the  heat  and  the  power  can  be  taken 
from  one  boiler.  In  larger  plants  the  heating  boilers  are 
operated  on  the  low  pressure  and  the  power  boilers  on 
the  high  pressure  system.  In  the  high  pressure  system 
steam  goes  to  the  engine  and  pumps  and  is  exhausted 
through  an  oil  separator  into  the  low  pressure  system. 
The  pressure  of  the  exhaust  is  determined  by  the  pres- 
sure carried  on  the  low  pressure  system.  This  system 
is  particularly  desirable  where  the  heating  load  is  con- 

193 


Notes 


o  n 


Heating         and          Ventilation 


siderably  larger  than  the  power  load;  and  where  at 
times  the  engines  are  entirely  shut  down  and  only  the 
low  pressure  system  is  operated.  Fig.  69  shows  a 
sketch  of  this  arrangement. 


Fig.   69.  4 

Method  of  Carrying  Pipes. — In  carrying  pipes  from 
CMC  building  to  another  it  is  always  desirable,  if  possi- 
ble, to  carry  them  underground.  Carrying  underground 
affords  much  tetter  heat  insulation,  the  pipes  are  more 
easily  supported  and  are  less  apt  to  be  disturbed.  The 
simplest  method  of  underground  distribution  and  the 
cheapest  is  to  enclose  the  pipes  in  a  pine  board  case,  as 
shown  in  Fig.  70.  This  arrangement,  however,  is  not 
as  desirable  as  a  tunnel  system,  the  heat  insulation  is 
not  as  satisfactory  and  the  pipes  are  more  difficult  to 
get  at  for  repairs.  Its  chief  recommendation  is  that  it 
is  cheap.  In  most  cases  it  should  be  used  for  work 
where  the  expense  of  a  tunnel  system  would  not  be  war- 
ranted. 


194 


Notes 


on          Heating         and 


Ventilation 


A  system  quite  largely  used  is  to  enclose  pipes  in 
pump  logs,  that  is,  hollow  wooden  pipes.  These  pipes 
are  creosoted  and  filled  with  an  asphalt  paint  or  some 
other  means  of  preservation.  They  are  often  lined  with 
tin  or  some  other  form  of  metal  lining.  The  pipe  is 
passed  through  the  pump  log  and  is  usually  covered  with 
about  one  inch  of  some  standard  form  of  pipe  cover- 


f/a. 


Fig.   70. 


ing.  This  method  of  running  the  pipes  furnishes  quite 
satisfactory  heat  insulation.  It  is  much  more  durable 
than  the  pine  board  duct,  it  is  easier  to  install  and  easier 
to  replace  in  case  of  repairs.  It  has,  however,  the  dis- 
advantage of  making  the  pipe  quite  inaccessible  and  in 
case  of  accident  the  removal  of  the  entire  system  is 
necessary ;  this  in  many  places  is  very  expensive.  The 
builders  of  one  of  these  pipe  ducts  stated  that  the  loss 
in  the  pipes  enclosed  in  this  manner  is  from  one-fourth 
of  one  per  cent  to  six  per  cent  per  mile  of  pipe  deliver- 
ing steam  at  its  full  capacity.  The  larger  the  pipe  the 
smaller  the  proportional  heat  loss.  Fig.  71  shows  a 
cross  section  of  a  pipe  log  with  covering.  This  pipe 
log  construction  is  most  used  in  central  heating  systems 
for  building  connections  and  where  only  one  pipe  is  to 
be  used  in  supplying  the  building. 

Where  it  is  necessary  to  run  a  number  of  pipes  the 
most  desirable  method  is  to  run  through  tunnels  made 

195 


Notes          on          Heating          and          Ventilation 

of  brick  or  cement.  The  size  and  form  of  tunnel  used 
will  depend  upon  the  number  of  pipes  to  be  carried,  the 
character  of  the  soil  and  the  depth  into  the  ground. 
Where  tunnel  systems  have  been  installed  the  general 
experience  has  been  that  they  more  than  paid  for  them- 
selves in  a  short  time,  as  they  entirely  do  away  with 
the  necessity  of  taking  up  the  pipe  and  allow  for  repairs 


PS  an 


Fig.   71. 


and  frequent  inspection.  Fig.  72  shows  a  small  sized 
tunnel.  This  tunnel  has  been  used  for  carrying  pipes 
not  over  8  inches  in  diameter.  The  tunnel  is  3  feet  6 
inches  wide,  4  feet  6  inches  high.  It  is  made  of  brick 
4  inches  thick,  with  1  inch  of  Portland  cement  outside. 
This  cement  is  painted  a  thick  coat  of  tar  or  asphalt  to 
below  the  crown  of  the  arch.  Wherever  the  supports 
come  the  tunnel  is  ribbed  with  an  8-inch  rib  of  brick 
16  inches  wide.  This  rib  is  placed  about  every  10  feet. 
A  tunnel  of  this  kind  has  been  in  use  for  some  time  and 
has  given  good  satisfaction.  It  is  not  desirable  to  use 
this  sort  of  tunnel  for  large  pipe  or  where  the  tunnels 
are  to  be  frequently  inspected. 

For  larger  pipes  the  section  shown  in  Fig.  73.  is 
much  more  desirable.  This  tunnel  is  5  feet  by  6  feet 
inside  dimensions.  The  tunnel  is  made  of  two 

196 


Notes 


o  n 


Heating         and          Ventilation 


courses  of  brick  or  about  9  inches  thick.  It  is  plas- 
tered on  the  ontside  with  1  inch  of  cement  and  then 
tarred  down  to  the  crown  of  the  arch.  At  the  lowest 
point  of  the  tunnel  on  each  side  is  shown  a  3-inch  tile, 
which  serves  to  carry  away  the  drainage  around  the  tun- 
nel. If  possible,  this  3-inch  tile  should  be  brought  to 
some  drain.  In  moist  clay  soils  it  is  sometimes  found 


Fig.   72. 

necessary  to  run  a  tile  under  the  middle  of  the  tunnel, 
connecting  with  the  inside  of  the  tunnel  so  that  seepage 
through  the  tunnel  walls  may  be  carried  off  either  to 
the  sewer  or  to  the  pumping  plant.  In  sand  and  in 
gravel  soils  this  is  not  necessary,  as  almost  no  difficulty 

197 


Notes         on         Heating         and         Ventilation 

would  be  experienced  from  leakage.  Fig.  74  shows  a 
tunnel  made  for  carrying  two  large  pipes.  The  tunnel 
is  5  feet  6  inches  by  6  feet  6  inches  and  gives  ample 


Fig.   73. 

passageway  between  the  pipe  supports  for  easy  access 
at  all  times. 

The  cost  of  tunnels  depends  upon  the  nature  of  the 
excavation  and  the  price  of  materials.  To  give  an  ap- 
proximate idea  of  what  tunnels  cost,  the  tunnel  shown  in 

198 


Notes          on          Heating          and          Ventilation 

Fig.  72  has  been  constructed,  including  excavation,  back 
filling  and  all  necessary  material,  for  $7.00  per  linear 
foot.  The  tunnel  shown  in  Fig.  73  has  been  constructed 
for  $8.00  per  linear  foot,  and  the  tunnel  shown  in  Fig.  70 
has  been  constructed  for  $9.00  per  linear  foot. 


Fig.   74. 

Sizes  of  Pipes. — The  size  of  the  pipe  necessary  to 
carry  a  give'n  quantity  of  steam  is  determined  by  the 
allowable  loss  of  pressure  that  the  system  will  permit. 
In  a  low  pressure  system  this  loss  of  pressure  should 
not  exceed  2  pounds.  In  a  high  pressure  system  it  should 

199 


Notes          on          Heating         and          Ventilation 

not  exceed  10  pounds.     The  rule  most  commonly  used 

is  called  Babcock's  rule,  and  is  as  follows: 

Let  W  —  weight  of  steam  in  pounds  flowing  per  minute. 

w  =  the  weight  of  a  cubic  foot  of  steam. 

pj  =  pressure  in  pounds  per  square  inch  of  steam  enter- 
ing pipe. 

p2  =  pressure  in  pounds  per  square  inch  of  steam  leav- 
ing the  pipe. 

d  =  diameter  in  inches. 

L  =  length  of  pipe  in  feet. 

w  (Pi  —  P2)  dr, 

Then  W  =  87    L  (1  + — ) 

d 

The  best  way  of  handling  'this  expression  is  to 
assume  different  diameters  of  pipe  and  then  try  a 
number  of  standard  pipe  sizes.  In  this  way  deter- 
mine the  pipe  size  which  approximates  most  closely 
the  weight  of  steam  which  it  is  desired  to  carry. 

In  IDW  pressure  gravity  return  systems  the  return 
is  usually  taken  as  one-half  the  pipe  size  of  the  steam 
main  up  to  10  inches.  Above  10  inches  the  size  is 
taken  as  one-half  the  size  of  the  steam  main  minus 
one  size.  As,  for  example,  a  10-inch  main  would 
require  5-inch  return,  a  14-inch  would  require  a  6- 
inch  return.  The  size  of  drip  main  for  a  given  steam 
main  depends  entirely  upon  the  length  of  the  main. 
It  should  never  be  less  than  ^4-inch  and  it  is  seldom 
necessary  to  make  the  pipe  over  1^4 -inch.  A  1^4- 
inch  drip  main  will  take  care  of  2,000  feet  of  12-inch 
pipe,  providing  the  pipe  is  well  covered  with  stand- 
ard covering. 

200 


Notes          on          Heating          and          Ventilation 

Hangers  and  Anchors. — When  pipes  are  carried 
through  tunnels  it  is  necessary  to  provide  a  different 
form  of  hanger  than  in  building  work.  In  tunnel 
work  the  head  room  is  so  limited  it  is  ordinarily  im- 
possible to  suspend  pipes  from  above  and  they  must 
have  some  form  of  roller  hanger.  Fig.  74  shows  ball- 
bearing hangers  for  12-inch  pipe  and  roller  hangers 
for  the  6-inch  pipe.  Fig.  72  shows  a  very  simple 
form  of  roller  hanger.  Fig.  73  also  shows  a  form  of 
ball-bearing  hanger  for  8-inch  pipe  and  roller  bearing 
for  4-inch  pipe.  The  ball-bearing  hangers  shown  in 
these  figures  have  given  very  satisfactory  results. 
They  are  expensive,  but  the  expense  is  warranted. 
In  tunnel  work  the  clearance  is  so  small  that  it  is 
necessary  to  know  exactly  where  the  expansion  is 
to  be  taken  up.  The  only  way  to  be  certain  of  this  is 
to  anchor  the  pipe  at  the  point  desired.  These  an- 
chors are  usually  made  of  heavy  cast  iron  with 
wrought  iron  straps  enclosing  the  pipe.  The  hangers 
should  be  built  into  the  tunnel  or  building  walls  and 
should  pass  entirely  through  the  wall,  projecting  4 
inches  or  more  on  the  opposite  side  of  the  wall.  The 
anchors  should  not  be  built  into  walls  that  are  less 
than  12  inches  thick,  and  preferably  they  should  be 
16  inches  thick.  In  putting  in  hangers  and  supports 
in  tunnel  work  it  is  a  very  important  thing  to  see 
that  a  clear  space  is  left  through  the  center  of  the 
tunnel  which  will  give  easy  access  to  the  tunnel.  The 
easier  the  access  and  the  more  comfortable  the  tun- 
nel for  passage,  the  more  frequent  will  be  the  in- 
spections, and  such  inspections  insure  of  the  piping 
being  kept  in  the  best  possible  condition. 

30X 


Notes 


on          Heating         and          Ventilation 


Air  Valves. — Fig  75  shows  an  air  valve  adapted  for 
use  on  large  heating  systems.  The  outlet  of  this  air 
valve  is  three-quarters  of  an  inch  in  diameter.  It  is 
particularly  designed  to  take  care  of  the  air  in  the 


,  LET   |    PIPE 

Fig.   75.     Air   Valve  for   Use   on   Steam    Mains. 

building  and  tunnel  mains.  The  ordinary  sized  valve 
used  in  radiators  is  entirely  insufficient  to  take  care 
of  large  mains.  Piping  that  is  4  inches  and  over 
should  have  the  larger  valves.  With  still  larger  pip- 
ing, 10  or  12  inches  in  diameter,  where  the  mains  are 
400  or  500  feet  long,  even  this  size  is  hardly  sufficient 
to  take  care  of  the  air  unless  a  number  of  them  are 
used. 

The  valve  shown  in  Fig.  76  is  often  used.  This 
consists  of  a  brass  pipe  "A"  four  feet  long,  to  which 
is  screwed  a  1^-inch  angle  valve.  This  pipe  and 
angle  valve  are  attached  by  a  suitable  elbow  and 


Notes 


on          Heating         and          Ventilation 


nipple  to  the  main  from  the  point  at  which  the  air  is 
to  be  removed.  A  yoke  is  fastened  at  elbow  "B" 
and  to  this  yoke  two  iron  rods  are  attached.  These 


Fig.  76.— This  Form   of  Air  Valve  is  Often   Used. 

iron  rods  are  connected  at  the  other  end  of  the  yoke 
"C."  '  Yoke  "C"  is  attached  to  the  valve  stem  of  the 
angle  valve.  The  threads  are  removed  from  the  stem 


203 


Notes          on          Heating          and          Ventilation 

of  the  valve  so  that  the  valve  will  pass  freely  through 
the  stuffing  box.  By  means  of  a  lock  nut  on  the  valve 
stem  the  height  of  the  valve  disc  above  the  seat  may 
be  adjusted.  To  start  with,  however,  the  brass  rod 
"A"  will  be  cold  and  the  valve  disc  will  be  off  the 
valve  seat  and  air  will  be  alowed  to  pass  out  pipe 
"D."  As  soon  as  steam  comes  the  brass  pipe  "A"  ex- 
pands, bringing  the  valve  seat  up  against  the  disc  and 
closing  the  valve  so  that  no  steam  can  escape. 


Fig.  77.     Air  Valve  to   Relieve  a   Fitting  and   Line  of  Pipe  from  Air. 

Another  arrangement  that  may  be  used  is  shown  in 
Fig.  77.  At  the  point  at  which  it  is  desired  to  re- 
move the  air  a  1-inch  pipe  is  tapped  into  the  fitting. 
Into  this  is  tapped  a  1-inch  nipple,  an  elbow  and  a 
short  piece  of  pipe,  as  shown.  At  the  end  of  this 
short  piece  of  pipe  is  attached  a  gate  valve.  At  inter- 
vals along  the  inside  of  the  pipe  are  attached  large  air 
valves,  such  as  the  one  shown  in  Fig.  75.  On  start- 
ing up  the  system  the  gate  valve  is  left  wide  open 
and  remains  open  until  steam  begins  to  blow,  then 
this  gate  valve  is  closed  and  the  small  air  valves  take 

304 


Notes          on          Heating         and          Ventilation 

care  of  the  accumulation  of  air  that  occurs  from  time 
^o  time. 

Lack  of  proper  air  valves  may  cause  serious  acci- 
dents in  the  pipe  system.  In  large  pipes  when  steam 
is  turned  on  it  will  circulate  along-  the  top  of  the 
pipe  and  the  cold  air  remains  at  the  bottom  of  the 
pipes;  the  upper  side  of  the  pipe  will  then  be  hotter 
than  the  lower  and  hence  will  expand  more  than  the 
under  side.  The  tendency  of  the  pipe  is  to  assume  a 
circular  form,  as  shown  in  Fig.  78  by  dotted  lines.  In 


Fig.    78.      How    Air   Collects   and    Sometimes    Breaks   a    Piping   Sys- 
tem.      How    It    Is    Prevented. 

case  of  a  very  large  pipe  this  has  been  known  to 
wreck  the  piping  system,  breaking  flanges  and  spring- 
ing the  valve  seats.  Such  a  condition  may  be  pre- 
vented by  running  the  air  pipes  on  the  mains  down  to 
the  bottom  of  the  main,  as  shown  in  the  figure,  so 
that  the  air  is  removed  from  the  bottom  of  the  main 
instead  of  from  the  top  of  the  main.  In  long  piping 
systems  it  is  very  desirable  that  at  intervals  of  not 
more  than  100  feet  air  valves  should  be  placed  to 
remove  the  air  from  the  bottom  of  the  main.  The 
size  of  these  valves  will  depend  upon  the  size  of  the 
main  and  they  should  be  of  ample  capacity.  It  is 
not  always  necessary  to  use  automatic  valves.  Auto- 

205 


Notes          on          Heating          and          Ventilation 


matic  valves   can   be   replaced  by   ^-inch   or  %-i 
valves  for  this  purpose. 

Air  valves  should  be  located  at  all  high  points  on 
the  return  main,  particularly  at  points  where  the 
return  main  rises,  passes  along  the  horizontal,  and 
then  drops  down  again.  At  such  points  air  valves 
should  be  located  at  the  top  of  the  main.  If  this  is 
not  done  the  air  will  accumulate  at  these  high  points 
and  prevent  passage  of  water,  sometimes  almost  as 
effectively  as  though  the  main  were  valved  at  these 
points. 

Surge  tanks,  traps  and  other  devices  where  air  may 
accumulate  should  be  provided  with  air  valves.  In 
fact,  when  trouble  is  experienced  in  a  steam  pipe  sys- 
tem one  of  the  first  things  that  the  builder  should 
assure  himself  of  is  that  the  air  is  being  properly 
removed  from  all  parts  of  the  system. 

COMBINATION  OF  STEAM  AND  HOT  WATER 
SYSTEM. 

There  are  a  number  of  systems  using  a  combina- 
tion of  exhaust  steam  and  hot  water  for  use  in  con- 
nection with  central  heating  systems.  The  exhaust 
from  the  engine  is  passed  through  an  exhaust  heater 
and  the  water  heated  in  this  heater  is  circulated 
through  the  heating  system  by  means  of  a  pump.  In 
this  way  exhaust  steam  can  be  used  for  heating  a  large 
territory  without  producing  any  back  pressure.  This 
form  of  heating  may  be  used  in  connection  with  a 
condensing  engine.  The  water  being  circulated  by  a 
pump  under  pressure  insures  its  actual  circulation 
throughout  the  whole  system  and  makes  possible  the 
use  of  relatively  small  mains  for  heating  purposes, 

206 


Notes         on         Heating         and         Ventilation 

smaller  than  would  be  required  for  either  low  pres- 
sure steam  or  exhaust  steam.  In  addition  to  the  ex- 
haust steam  heater  there  may  be  used  either  a  hot 
water  boiler  or  an  auxiliary  live  steam  heater,  so  that 
in  case  the  exhaust  is  insufficient  for  heating  the 
water,  the  water  may  be  passed  through  this  live 
steam  heater,  bringing  it  up  to  the  proper  tempera- 
ture. In  some  cases  a  Greene  economizer  has  been 
used  for  furnishing  additional  heat,  thereby  making 
use  of  the  waste  from  the  boiler. 

Systems  of  this  kind  have  been  installed  in  a  num- 
ber of  cities  and  as  high  as  one  thousand  houses 
heated  from  a  central  heating  system.  In  these  hot 
water  circulating  systems  two  general  forms  of  pump 
are  used,  either  a  centrifugal  pump  driven  by  a  mo- 
tor or  engine,  or  a  piston  pump  of  the  ordinafy  type. 
In  most  cases  unless  a  high  pressure  is  desired,  a 
centrifugal  pump  is  desirable.  The  central  hot  water 
heating  system  has  one  particularly  desirable  feature 
— the  hot  water  leaving  the  system  may  be  adjusted 
to  correspond  with  the  external  temperature.  The 
size  of  hot  water  mains  is  determined  from  the  ve- 
locity of  water  circulating  in  the  main.  In  small 
mains  it  should  not  exceed  2  feet  per  second ;  in  large 
mains  it  may  be  as  high  as  4  feet  per  second. 

Central  heating  by  means  of  hot  water  is  particu- 
larly adapted  for  residence  districts,  as  the  system 
can  be  installed  with  less  expense  per  foot  of  main, 
making  it  possible  to  cover  profitably  an  area  having 
the  houses  scattered.  Central  heating  with  steam  is 
particularly  adapted  for  close  business  districts  where 
steam  is  the  usual  form  of  heating  and  where  the 
piping  system  will  be  relatively  short  for  the  load 
carried. 

207 


Notes         on          Heating         and         Ventilation 

In  connection  with  the  systems  using  pressure 
there  must  be  used  some  form  of  expansion  tank. 
Some  of  these  systems  use  an  open  expansion  tank, 
allowing  the  water  in  the  return  system  to  enter  this 
open  tank  at  practically  atmospheric  pressure,  the 
suction  of  the  circulating  pump  being  connected  to 
this  open  tank.  Where  this  system  is  used  a  piston 
type  of  pump  would  probably  be  a  desirable  form. 
Where  the  centrifugal  type 'of  pump  is  used  it  would 
be  desirable  to  use  a  closed  tank.  In  this  case  the 
tank  is  partly  filled  with  water  and  partly  filled  with 
air.  The  expansion  and  compression  of  the  air  al- 
lows "for  the  change  in  the  volume  of  water  due  to 
changes  of  temperature  conditions.  In  this  case  the 
pump  will  then  only  furnish  the  pressure  necessary 
to  overcome  the  resistance  of  the  piping  system.  The 
air  side  of  the  expansion  tank  should  be  provided 
with  an  air  pump,  so  that  pressure  may  be  maintained 
by  means  of  an  air  pump  on  the  air  side  of  the  sys- 
tem and  the  proper  quantity  of  air  carried  in  the  tank 
at  all  times. 


BOS 


CHAPTER  XIII. 

PIPING,  COVERING  AND  OTHER 
APPLIANCES. 

Pipe  Covering. — In  all  piping  installation  it  is  cus- 
tomary to  cover  the  distributing  pipes,  except  ra- 
diator connections.  It  is  good  practice  to  cover  the 
risers  passing  through  buildings,  together  with  all 
steam  and  return  mains.  Where  the  water  mains 
pass  through  rooms  in  which  any  drip  from  the  pipes 
would  be  objectionable,  such  pipes  are  also  covered 
to  prevejit  the  condensation  of  moisture  on  the  out- 
side of  pipes.  In  general  the  best  form  of  non-con- 
ductor is  dry  air,  which  is  so  confined  as  to  prevent 
circulation.  In  all  successful  forms  of  covering  air 
is  confined  -in  the  structure  of  the  covering  and  the 
effectiveness  of  the  covering  depends  largely  upon 
the  confining  of  this  air.  The  effectiveness  of  differ- 
ent forms  of  covering  was  determined  in  a  series  of 
experiments  made  under  the  direction  of  Prof.  M.  E_ 
Cooley,  University  of  Michigan.  Table  LII  shows  the 
relative  effectiveness  of  some  of  the  different  forms 
of  covering. 

The  results  of  these  tests  show  that  hair  felt  is  the 
best  non-conductor.  It  is  not,  however,  suited  for 
over  5  pounds  pressure,  as  it  chars  and  breaks  down 
at  higher  pressure  owing  to  the  higher  temperature;: 
this  is  also  true  of  the  wool  felts.  In  low  pressure- 
work  at  such  temperatures  as  are  ordinarily  used,, 
hair  felt  is  found  to  be  quite  satisfactory.  It  is  ex- 
pensive, but  its  expense  is  warranted  in  the  saving 
from  condensation  in  the  piping. 

209 


Notes         on         Heating         and         Ventilation 

TABLE   LII. 
Relative  Value  of  Different  Pipe  Coverings. 

Ill  '        L!  it  t   i  * 

;>  *i  °    i!  ii. 


M!  id  Ii  si  IK 

Material  of  covering 
Moulding  coverings. 

1.  Asbestos  .................  145          .319          1.23          136.  .803 

2.  Magnesia    ................  119  .224  .94  166.  .915 

3.  Magnesia   and   asbestos.     .125          .300          1.12          118.          .879 

4.  Asbestos  and  wool  felt..     .190          .228          1.12          102.  .910 

5.  Wool   felt   ................  117          .234          1.16          110.          .904 

6.  Wool  felt  and  iron  with 

air  space   ..............  134  .269  ...  125.  .828 

Sectional  Coverings. 

7.  Mineral  wool  .............  097  .193  .94  91.  .952 

8.  Asbestos  sponge  .........  105  .220  1.12  102.  .920 

9.  Asbestos  felt   ............  100  .217  1.35  94.  .923 

10.  Hair  felt  .................  080          .186          1.45  75.  .960 

Non-S'ectional  Coverings.  / 

11.  Two       layers       asbestos 

paper  ..................  388          .777  ...  364.  .263 

12.  Two       layers       asbestos 

paper,  one  inch  hair 
felt  and  one  thickness 
canvas  .................  070  .150  ...  68.  1.000 

Table  LIII  shows  the  relative  effectiveness  of  differ- 
ent thicknesses  of  covering.  Column  3  of  this  table 
shows  the  relative  effectiveness  of  the  various  thick- 
nesses of  covering  compared  with  the  bare  pipe.  From 
this  table  it  is  not  a  difficult  matter  to  figure  the 
amount  of  saving  that  may  be  made  by  using  various 

TABLE   LIII. 

Heat  Transmission  for  Varying  Thicknesses  of  Covering. 
Condensation      Ratio  of  Conden-        B.  T.  U.'S 
Thickness  of      per  sq.  ft.  per      sation  covered    transmitted  per 
covering.        hour  in  pounds.      to  bare  pipe.      sq.  ft.  per  hour. 
inches. 

%  .120  .281  167. 

%  .117  .255  163. 

1  .107  .231  149. 
1%                          .099                             .219  138. 
1%                           087                             .191                             121. 

2  '-078  .19  108. 

The  covering  used  in  obtaining  the  above  results  was  a  wool  felt. 

210 


Notes         on         Heating         and         Ventilation 

thicknesses  of  covering.  Knowing  the  amount  of 
steam  carried  per  year  and  the  cost  to  produce  1,000 
pounds  of  steam,  and  having  the  results  shown  in 
this  table,  we  can  easily  compute  the  financial  saving 
to  be  made  in  the  various  thicknesses  of  covering. 
In  doing  this  it  is  usually  found  that  for  building 
work  an  inch  covering  is  sufficiently  heavy;  but  for 
tunnel  work  and  all  work  where  the  heat  loss  from 
the  pipe  is  entirely  lost  and  does  not  enter  the  build- 
ing it  is  economy  to  use  covering  2  inches  thick. 
Where  superheated  steam  is  used  at  high  tempera- 
tures the  covering  is  from  3  to  5  inches  thick.  Table 
LIV  shows  the  heat  lost  through  a  1-inch  wool  cover- 
ing with  various  steam  pressures.  In  covering  a  pip- 
ing system  the  fittings  and  valves  should  be  covered 
the  same  thickness  as  the  pipe.  This  also  applies  to 
flanges  and  steam  traps.  Where  flanges  and  other 
parts  which  require  removal  are  covered  they  should 
be  covered  so  that  the  covering  can  be  taken  off 
easily.  A  satisfactory  method  of  doing  this  is  to 
form  a  covering  composed  of  one  layer  of  asbestos 
paper,  1  inch  of  hair  felt  and  one  thickness  of  8- 
ounce  duck.  These  are  quilted  together  with  cord  so. 
that  the  jacket  is  firmly  held  in  one  piece.  This  cov- 
ering is  then  fastened  over  the  pipe  to  be  covered 
by  means  of  hooks  and  laces. 

TABLE  LIV. 
Heat  Transmission  for  Varying  Pressures. 

Condensation      Ratio  of  Conden-  B.  T.  U.'s  Trans- 
Gauge                   per  sq.          sation  of  covered  mission  per 
pressure.          ft.  per  hour.           to  bare  pipe.  sq.  ft.  per  hour. 
5.3                         .108                             .239  100. 
9.6                         .111                             .233  104. 
15.5                        .126                             .227  110. 
20.5                         .134                             .223  119. 

The  advantage  of  covering  may  be  shown  from  the 
following  computation : 

Sit 


Notes         on         Heating         and         Ventilation 

Example. — In  a  given  steam  plant  it  was  found 
that  the  heat  lost  from  bare  pipes  per  hour  was 
3,355,000  B.  t.  u.  In  the  particular  plant  in  ques- 
tion the  number  of  heat  units  required  to  make  a 
pound  of  steam  was  990,  and  this  loss  of  heat  would 
represent  a  condensation  of  3,390  pounds  of  steam 
per  hour.  Assuming  an  evaporation  of  9  pounds  of 
steam  per  pound  of  coal  this  would  be  equivalent  to 
376  pounds  of  coal  per  hour.  If  the  plant  were  op- 
erated 365  days  in  the  year  and  20  hours  a  day,  and 
the  coal  cost  $3.25  per  ton,  the  yearly  loss  would  be 
$2,069.  By  covering  the  pipe  1  inch  thick  with  hair 
felt  the  loss  which  would  result  from  the  bare  pipe 
would  be  reduced  to  15  per  cent,  which  equals  $314, 
making  a  saving  of  $1,755  by  putting  on  covering. 
This  amount  capitalized  at  10  per  cent  would  repre- 
sent an  investment  of  $17,550.  In  the  particular  case 
in  question  the  actual  cost  of  the  covering  was  but 
$3,500. 

Air  Valves. — In  steam  piping  work  it  is  very  im- 
portant that  the  piping  system  be  provided  with  suf- 
ficient number  of  properly  located  air  valves.  Pri- 
marily, air  valves  should  be  located  at  the  points  in 
the  piping  at  which  air  accumulates  in  quantity.  We 
are  familiar  with  the  fact  that  when  a  radiator  is  not 
provided  with  an  air  valve  steam  will  not  circulate 
into  it  and  it  does  not  become  warm.  This  is  also 
true  of  both  steam  mains  and  the  return  system.  The 
writer  has  seen  the  entire  return  system  of  a  building 
plugged  with  air  on  account  of  there  being  no  air 
valve  on  a  high  point  in  the  return  main. 

For  radiators  an  air  valve  similar  to  that  shown 
in  Fig.  79  is  usually  used.  You  will  notice  that  this 

212 


Notes          on          Heating         and         Ventilation 


air  valve  allows  air  entering  from  the  connection  to 
the  radiator  to  pass  directly  to  the  top  of  the  air  valve 
body  and  out  through  a  small  hole  or  opening,  which 
may  be  adjusted  by  means  of  a  screw  plug.  If  water 
enters  the  air  valve,  the  water  will  rise  in  the  valve 
body  until  the  copper  float,  having  a  pin  on  its  upper 
end,  rises  so  as  to  close  the  exit  from  the  air  valve, 


Fig.   79.    Type   of   Air    Fig.    80.       Air    Valve  Fig.    81.       Air    Valve 

Valves      Commonly        Used    on    Radiators  Adapted      to       Hot 

Used    in    Radiators.        In   Connection  with  Water  Work. 
Paul   Valve. 

and  no  water  is  allowed  to  escape.  When  steam  en- 
ters the  air  valve  the  expansion  plug  shown  at  th^ 
center  of  the  air  valve  expands,  raising  the  copper 
float,  again  closing  the  outlet  from  the  air  valve. 

Fig.  80  shows  an  air  valve  which  is  used  for  radi- 
ators in  connection  with  a  system  of  air  piping  from 
the  air  valves.  (1)  is  a  cap  screw  screwed  down  on 
the  valve  with  a  lead  washer,  making  a  tight  seat. 

(2)  is  a  hollow  screw  upon  which  the  expansion  post 

(3)  sets,  closing  the  valve.     The  adjustment  of  the 
valve  is  done  with  screw   (2),  and  this  may  be  done 

213 


Notes          on          Heating         and         Ventilation 

without  disturbing  the  valve.  (3)  is  a  hollow  part 
fastened  at  (5)  and  held  in  place  by  the  union  (6). 
This  should  never  be  'disturbed.  (4)  is  the  nipple  of 
the  valve  body,  by  which  it  is  attached  to  the  ra- 
diator. This  is  the  union  for  attaching  to  the  piping 
of  the  Paul  system  or  other  air  piping  system.  (7) 
is  a  nut  which  forms  the  union  for  attaching  this  pip- 
ing. The  operation  of  the  valve  is  as  follows :  The 
air  is  drawn  in  from  the  radiator  through  nipple  (4) 
into  the  valve  between  the  adjusting  screw  (2)  and 
the  composition  part  (3)  passing  down  through  (3) 
into  the  pipe.  When  steam  enters  the  composition 
part  becomes  heated  and  expands,  thereby  closing  the 
opening  between  (3)  and  (2).  When  air  again  ac- 
cumulates and  cools  this  composition  part  contracts, 
permitting  air  to  be  drawn  through  the  tube. 

There  are  two  typical  forms  of  air  valve,  one  clos- 
ing off  the  air  by  the  action  of  the  float,  the  other 
closing  off  the  air  by  the  action  of  heat  expanding 
a  plug.  Fig.  79  shows  a  combination  of  these  two 
principles,  which  prevents  the  throwing  of  water  or 
the  discharging  of  steam. 

Fig.  80  exemplifies  the  simple  expansion  operation. 
The  valve  shown  in  Fig.  80  would  allow  cold  water 
to  pass. 

Fig.  81  shows  an  air  valve  particularly  adapted  to 
hot  water  work.  In  this  air  valve  the  float  principle 
alone  is  used.  Air  enters  in  through  the  connection 
to  the  radiator,  as  shown  by  the  arrow  in  the  cut, 
passes  under  the  float  and  escapes  through  a  small 
tube  which  reaches  to  a  point  near  the  top  of  the  air 
valve.  As  soon  as  the  water  enters  the  float  lifts,  due 
to  the  air  compressed  by  the  water  under  the  float, 

214 


Notes 


o  n 


Heating         and         Ventilation 


Table  LV. 

WROUGHT  IRON  AND  STEKL  STEAM,  GAS  AND  WATER  PIPE 

TABLE  OF  STANDARD  DIMENSIONS 

Diameter 

Circum- 
ference 

Transverse 
Areas 

Length  of 
Pipe  per 
Sq  Ft  of 

Length  of  Pipe 
Containing 
One  Cubic  Foot 

£  Nominal  Weight 
g  pT  Per  Foot 

Number  of  Threads 
Per  Inch  of  Screw 

Nominal 
Internal 

Actual 
External 

Approximate 
Internal 
Diameter 

External 

Internal 

Internal 

§ 

Fxternal 
Surface 

Internal 
Surface 

In. 

In. 

In. 

In. 

In. 

ft: 

8: 

Ft. 

Ft. 

Ft. 

.405 

.27 

1.272 

.848 

.0573 

.0717 

9.44 

14.15 

2513. 

27 

M 

.54 

.364 

1.696 

1.144 

.1041 

.1249 

7.075 

10-49 

1?83.3 

.42 

18 

% 

.675 

.494 

2.121 

1.552 

.1917 

.1663 

5.657 

7.73 

751.2 

.559 

18 

K 

.84 

.623 

2.639 

1.957 

.3048 

.2492 

4.547 

6.13 

472.4 

.837 

14 

H 

1.05 

.824 

3.299 

2  589 

.5333 

.3327 

3.637 

4.635 

270. 

1.115 

14 

1 

1.315 

1.048 

4.131 

3.292 

.8626 

.4954 

2.904 

3.645 

166.9 

1.668 

UK 

IN 

1.66 

1.38 

5.215 

4.335 

1.496 

.668 

2.301 

2.768 

96.25 

2.244 

UK 

IK 

1.9 

1.611 

5.969 

5.061 

2.038 

.797 

2.01 

2.371 

70.66 

2.678 

UK 

2 

2.375 

2.067 

7.461 

6.494 

3.356 

1.074 

1.608 

1.848 

42.91 

3.609 

UK 

2K 

2.875 

2.468 

9.032 

7.753 

4.784 

1.708 

1.328 

1.547 

30.1 

5.739 

8 

3 

3.5 

3.067 

10.996 

9.636 

7.388 

2  243 

1.091 

1.245 

19.5 

7.536 

8 

3K 

4. 

3.548 

12.566 

11.146 

9.887 

2.679 

.955 

1.077 

14.57 

9.001 

8 

4 

4.5 

4.026 

14.137 

12.648 

12.73 

3.174 

.849 

.949 

11.31 

10.665 

8 

4K 

5. 

4.508 

15  708 

14  162 

15.961 

3.674 

.764 

.848 

9.02 

12.49 

8 

5 

5.563 

5.045 

17.477 

15.849 

19.99 

4.316 

.687 

.757 

7.2 

14.502 

8 

6 

6.625 

6.065 

20.813 

19.054 

28.888 

5.584 

.577 

.63 

4.98 

18.762 

8 

7 

7.625 

7.023 

23.955 

22.063 

38.738 

6.926 

.501 

.544 

3.72 

23.271 

8    * 

8 

8.625 

7.982 

27.0% 

25.076 

50.04 

8.386 

.443 

.478 

2.88 

28.177 

8 

9 

9.625 

8.937 

30.238 

28.076 

62.73 

10.03 

.397 

.427 

2.29 

33.701 

8 

10 

10.75 

10.019 

33.772 

31.477 

78.839 

11  .924 

.355 

.382 

1.82 

40.065 

8 

11 

11.75 

11. 

36.914 

34.558 

95.033 

13.401 

.325 

.347 

1.51 

45.028 

8 

12 

12.75 

12. 

40.055 

37.7 

113.098 

14.579 

.299 

.319 

1.27 

48.985 

8 

Piping  is  often  designated  as  "Merchant  Pipe."    This  term  is  used  to  indi- 
cate soft  steel  pipe  taken  from  stock.  In  sizes  from  ^  inch  to  6  inch  it  is  about  5r* 
under  the  card  weight  and  about  10$  under  card  weight  for  sizes  above  6  inch. 
Full  weight  pipe  is  made  of  stock  that  will  produce  pipe  of  full  card  weight. 

215 


Notes          on          Heating         a  n'd          Ventilation 

and  the  rubber  valve  held  by  the  rim  closes  the  open- 
ing- through  which  the  air  escapes.  The  valve  as 
shown  here  is  made  for  connection  to  an  air  valve 
piping  system.  A  similar  valve  is  made  without  this 
connection.  In  the  air  valve  shown  for  connection 
to  a  piping  system  there  is  a  three-way  plug  cock  in 
the  air  valve,  which  allows  of  air  and  water  being 
drawn  directly  to  the  air  pipe  system  and  of  being  en- 
tirely closed  off. 

Pipe. — Piping  for  heating  systems  is  made  either 
of  wrought  iron  or  mild  steel.  An  extra  price  must 
be  paid  for  wrought  iron  pipe.  The  smaller  sized 
pipes  up  to  and  including  1%  inches  are  butt  welded 
and  are  tested  to  300  pounds  pressure.  Large  sizes 
are  lap  welded  and  tested  to  500  pounds  pressure. 

Pipe  is  shipped  in  lengths  of  from  16  to  20  feet  and 
is  threaded  at  both  ends,  but  a  coupling-  is  put  on 
only  at  one  end. 

The  standard  size  pipes  in  use  are  given  in  ta- 
ble No.  LV. 

Piping  is  often  designated  as  "Merchant  Pipe." 
This  term  is  used  to  indicate  soft  steel  pipe  taken 
from  stock.  In  sizes  from  %-inch  to  6-inch  it  is  about 
5  per  cent  under  the  card  weight  and  about  10  per 
cent  under  card  weight  for  sizes  above  6-inch. 

Full  weight  pipe  is  made  of  stock  that  will  produce 
pipe  of  full  card  weight. 

Both  steel  and  wrought  iron  piping  is  designated 
as  wrought  iron  pipe.  If  wrought  pipe  is  desired  it 
should  be  called  "strictly  wrought  iron  pipe." 

Piping  is  made  in  three  weights — standard  pipe, 
the  dimensions  of  which  are  given  in  Table  42 ;  extra 

216 


Notes         on          Heating         and         Ventilation 


strong  pipe,  suitable  for  working  pressures  up  to  # 
pounds;  double  extra  strong  pipe,  suitable  for  work- 
ing pressvires  up  to  500  pounds. 

Fittings.  —  For  heating  work  standard  weight  cast  iron 
screwed  fittings  are  used  up  to  6  or  8  inches  in  diameter. 
Above  that  it  is  usual  to  use  flange  fittings. 

When  screwed  fittings  are  used,  flanges  must  be 
placed  in  the  piping  to  provide  for  disconnecting  in 
case  of  repairs.  In  screwing  pipes  into  fittings  the 
pipe  grease  should  always  be  placed  on  the  pipe 
threads  so  that  the  excess  will  not  be  left  in  the  fit- 
tings. 

In  describing  a  tee  always  give  the  dimensions  of 
the  "run"  first  and  of  the  side  outlet  last.  A  bullhead 
tee  is  one  in  which  the  side  outlet  is  larger  than  the 
outlets  in  the  "run." 

It  is  better  practice  to  use  reducing  elbows  or  re- 
ducing tees  than  to  use  standard  tee  or  elbows  and 
reduce  them  by  means  of  bushings. 

Valves.  —  Valves  2  inches  and  under  are  made  of 
all  brass  with  removable  discs.  For  radiators  where 
the  piping  comes  through  the  floor,  angle  valves  are 
used.  Where  the  piping  comes  over  the  floor  offset 
or  corner  offset  valves  are  used.  Gate  valves  should 
be  used  in  horizontal  lines  of  piping  which  carry  con- 
densation. Globe  valves  may  be  used  in  vertical  pipes 
but  not  in  horizontal  pipes,  as  they  dam  up  the  water 
passing  in  the  pipe. 

Where  check  valves  are  used  they  should  be  of  the 
swinging  check  pattern. 

Valves  above  2  inches  are  usually  used  with  iron  bod- 
ies and  brass  mountings  and  should  have  renewable  disc 
seats, 

817 


CHAPTER  XIV. 

AUXILIARY   DEVICES   FOR  HEATING 
SYSTEM. 

A  temperature  regulator  is  an  automatic  device 
which  will  open  and  close  the  valve  of  the  radiator 
so  as  to  keep  the  room  at  a  constant  temperature. 
The  temperature  regulator  in  general  consists  of  three 
parts.  First,  a  thermostat  which  is  so  constructed 
that  its  parts  will  move  with  a  change  of  temperature 
in  the  surrounding  air  and  the  motion  of.  these  parts 
will  directly  or  indirectly  open  the  dampers  or  valves 
which  control  the  heat  supply.  Second,  there  must 
be  some  means  of  transmitting  the  motion  from  the 
parts  of  the  thermostat  to  the  valves  or  dampers  con- 
trolling the  heat  supply.  Third,  some  form  of  me- 
chanism for  opening  the  valves  or  dampers.  In  most 
temperature  regulating  systems  the  thermostat  mere- 
ly furnishes  power  enough  to  close  or  open  an  air 
valve  or  electric  switch  and  thus  start  or  stop  the 
operation  of  the  valves  or  dampers. 

The  form  most  used  at  the  present  time  uses  com- 
pressed air  to  operate  the  valves  and  dampers.  In 
the  Johnson  thermostat  a  small  air  valve  is  opened 
by  the  expansion  of  a  curved  strip  composed  of  two 
materials  having  different  rates  of  expansion.  The 
bending  of  this  strip  due  to  change  of  temperature 
allows  the  air  to  escape  and  a  small  diaphragm  to 
move  back,  thus  opening  a  second  valve  allowing 
the  air  to  come  from  the  compressor  or  source  of 
air  supply  and  close  the  valve  or  damper  on  the 
radiator.  When  the  room  becomes  cool  the  contrac- 

218 


Notes 


on          Heating          and          Ventilation 


tion  of  this  strip  closes  the  first  small  valve  forcing 
out  the  diaphragm  and  closing  off  the  compressed 
air  supply  to  the  valve  or  damper  and  releasing  the 
air  already  in  the  valve  or  damper.  Another  form  of 
thermostat  extensively  used  is  operated  by  means 
of  a  liquid  confined  in  a  thin  metal  vessel,  the  liquid 


Fig.   82. 

having  a  very  high  degree  of  expansion.  As  the 
liquid  expands  or  contracts  it  controls  the  system  of 
valves  controlling  the  heat  supply  to  the  room. 

Temperature  regulation  is  a  desirable  thing  in  all 
large  heating  systems,  particularly  for  public  build- 

219 


Notes          on          Heating          and          Ventilation 

ings.  The  systems  are  quite  expensive,  but  the  ex- 
pense of  construction  is  more  than  offset  by  the  sav- 
ing in  fuel  bills.  The  saving  in  fuel  bills  in  most  cases 
is  not  less  than  15  per  cent  and  often  as  high  as  20  per 
cent.  In  general  the  operation  of  these  systems  has  been 
entirely  satisfactory  even  after  they  have  been  in  use 
some  time  without  any  attendance.  The  control  of  the 
temperature  of  the  room  should  be  regulated  within  3 
degrees.  With  proper  care  these  systems  should  con- 
trol the  temperature  of  the  room  within  2  degrees. 
Temperature  regulating  apparatus  is  particularly  de- 
sirable in  school  rooms ;  this  places  the  temperature 
of  the  room  outside  the  control  of  the  instructor  and 
it  is  then  free  from  his  own  personal  ideas  in  the 
matter,  thus  adding  much  to  the  health  and  comfort 
of  the  occupants  of  the  room.  With  the  fan  system  it  is 
difficult  to  get  satisfactory  operation  without  tempera- 
ture regulation.  The  application  of  temperature  regula- 
tion to  the  fan  system  is  shown  in  Fig.  83. 

Air  Piping  System.  The  discharge  of  air  from  the  air 
valves  and  radiators  often  produces  a  very  disagree- 
able odor  and  in  addition  it  is  very  difficult  to  obtain 
an  air  valve  which  will  not  at  times  discharge  a 
certain  amount  of  steam  or  water.  This  difficulty 
may  be  overcome  by  using  an  air  valve  so  designed 
that  the  discharge  connection  to  the  valve  can  be 
fastened  to  a  piping  system.  The  pipes  and  air  valves 
are  carried  to  the  basement,  collected  into  a  larger 
pipe  and  discharged  to  a  sewer  or  suitable  vessel. 
A  system  of  air  piping  is  very  desirable,  particularly 
in  large  buildings,  such  as  hotels  and  office  buildings, 
where  it  saves  materially  in  the  attendance  necessary 

230 


Notes          on          Heating         and         Ventilation 

to  keep  the  plant  in  operation.  It  is  also  desirable 
in  nice  residences  where  any  discharge  of  water  or 
steam  might  injure  the  furnishings.  In  case  it  is 
desirable  to  install  a  vacuum  system  of  heating  this 
system  could  be  connected  directly  to  a  vacuum  pump 
insuring  more  rapid  circulation  in  the  radiation. 

Damper  Regulators.  It  is  always  desirable  in  a 
steam  or  hot  water  heating  plant,  particularly  steam, 
to  install  some  form  of  damper  regulator  on  the 
boiler.  In  some  heating  plants  it  consists  of  an  ordi- 
nary rubber  diaphragm  enclosed  in  a  metal  case.  The 
steam  is  allowed  to  come  in  contact  with  one  side 
of  the  diaphragm,  pushes  a  lever  attached  to  the  other 
side  of  the  diaphragm.  This  lever  operates  a  damper 
controlling  the  air  supply  to  the  fire  and  sometimes 
also  operates  the  check  valve  in  the  breeching.  This 
is  a  very  desirable  arrangement,  as  it  reduces  the  at- 
tendance necessary  to  keep  the  pressure  in  the  boiler  at 
the  point  desired. 

Humidity  Regulation. — The  humidity  of  the  atmos- 
phere is  a  very  important  consideration  in  any  heating 
system.  When  the  air  is  very  dry  it  is  necessary  for  a 
room  to  have  a  much  higher  temperature  in  order  that 
it  may  feel  comfortable  than  when  the  air  is  moist.  It 
is,  therefore,  important  that  we  keep  the  humidity  at  a 
point  as  high  as  consistent  with  satisfactory  operation. 
Cold  air  contains  proportionately  less  moisture  than  warm 
air,  and  therefore  when  cold  air  is  heated  and  brought 
into  a  building  it  should  be  moistened  in  order  to  keep 
a  proper  per  cent  of  humiditv.  The  average  humidity 
is  about  70  per  cent,  in  the  arid  regions  humidity  may 
be  as  low  as  30  per  cent.  Humidity  as  low  as  30  per 


Notes 


o  n 


Heating         and         Ventilation 


cent  produces  irritation  of  the  lungs  and  smarting  of 
the  eyes.  In  cold  weather,  if  the  humidity  of  the  out- 
side air  is  70  per  cent  and  this  air  is  heated  and 
brought  into  the  room  without  moistening,  its  humid- 


ity may  be  reduced  as  low  as  30  or  35  per  cent,  mak- 
ing the  air  as  dry  as  in  the  most  arid  regions.  This 
produces  a  serious  effect  upon  the  inhabitants  and 
also  the  furniture  of  the  room.  The  decrease  of  hu- 
midity due  to  the  action  of  the  heating  system  occurs 
particularly  in  the  indirect  heating  system.  There 
has  been  placed  on  the  market  what  is  called  a  humid- 

222 


Notes 


o  n 


Heating 


and 


Ventilation 


ostat.  This  is  similar  to  a  thermostat  except  that  it 
is  arranged  so  that  as  the  moisture  decreases  in  the 
room  the  humidostat  opens  up  a  series  of  steam  or 
water  jets  in  the  air  supply  so  that  the  air  in  passing 


Fig.  83. 


through  the  steam  or  water  jet  takes  up  moisture. 
When  the  moisture  gets  to  a  certain  percentage,  deter- 
mined by  the  setting  of  the  humidostat,  the  apparatus 
closes  off  automatically  the  steam  or  water  jets.  Such 
devices  are  particularly  desirable  in  connection  with 
school  and  hospital  heating  plants. 

Air  Washers. — In   the   large   cities  the   smoke  and 
dust  in  the  air  makes  it  undesirable  to  introduce  this 

223 


Notes          on          Heating          and          Ventilation 

air  directly  into  the  room  for  ventilating  purposes.   A 
great  many  schemes  have  been  tried  to  remove  the 


Fig.    84. 


Notes         on          Heating         and         Ventilation 

dust  from  the  air.  The  earliest  form  was  to  use  bur- 
lap screens  through  which  the  air  passes.  These 
screens  work  fairly  well,  but  the  finer  dust  will  always 
be  carried  through  them.  A  better  plan  is  to  pass  the 
air  through  a  sheet  or  series  of  sheets  of  water.  After 
passing  through  these  sheets  of  water  the  air  is  passed 
through  an  apparatus  which  removes  the  excess  of 
water.  Fig.  84  shows  the  general  arrangement  of  an 
air  washing  system.  As  you  will  notice  from  the 
figure,  the  air  first  passes  through  a  tempering  coil 
which  raises  the  temperature  from  60  to  70  degrees, 
then  passes  through  the  sprays  or  sheets  of  water, 
then  through  the  eliminator,  where  the  excess  of  water 
is  removed,  and  then  it  passes  to  the  heating  coils  to 
be  heated.  The  water  used  for  washing  the  air  is 
circulated  over  and  over  again  by  means  of  a  small 
centrifugal  pump  driven  by  a  motor.  In  some  cases 
it  is  desirable  that  the  air  should  be  cooled.  This  may 
be  done  by  placing  cooling  coils  in  the  tank  where  the 
water  collects  after  having  washed  the  air,  and  reduc- 
ing the  temperature  of  this  water  to  the  desired  point 
or  by  washing  with  cold  water.  The  washing  of  the 
air  with  water  also  increases  the  humidity  of  the  air. 
In  a  plant  installed  by  the  author  the  humidity  of  the 
air  has  been  kept  at  a  point  not  lower  than  70  per  cent 
by  means  of  this  washer.  Air  washing  devices  are 
very  effective  in  removing  dirt ;  the  amount  of  dirt 
removed  in  some  cases  is  very  large. 

Vacuum  Heating  Systems. 

In  the  systems  of  steam  heating  that  have  been  de- 
scribed the  steam  has  been  used  at  a  pressure  higher 
than  that  of  the  atmosphere.  Plants  are  now  installed 

225 


Notes          on          Heating         and          Ventilation 

in  which  the  pressure  in*  the  radiator  may  be  atmos- 
pheric pressure  or  lower.  The  advantages  of  such  a 
system  are : 

First.  Where  exhaust  steam  is  used  the  heating 
will  not  increase  the  back  pressure  on  the  engines, 
but  may  reduce  the  back  pressure. 

Second.  The  air  can  be  completely  removed  from 
the  coils  and  radiators. 

Third.  There  is  perfect  drainage  through  the  re- 
turns, preventing  all  possibility  of  water  hammer. 

There  are  two  distinctly  different  types  of  vacuum 
heating  systems,  one  in  which  the  air  is  drawn  from 
the  radiator  by  means  of  an  air  pump  through  the  air 
valve,  as  shown  in  Fig.  75,  and  the  other  in  which  the 
radiator  is  fitted  with  a  special  form  of  return  valve 
and  vacuum  is  maintained  on  the  return  system  by 
means  of  a  pump  or  aspirator. 

The  best  example  of  the  first  type  is  the  Paul  sys- 
tem. In  this  system  the  air  valves  are  all  connected 
to  a  system  of  air  mains.  These  mains  extend  to  an 
air  ejector.  This  injector  may  be  operated  by  either 
steam  or  water.  The  advantage  of  this  system  de- 
pends principally  on  the  quick  removal  of  the  air  from 
the  piping  and  radiators.  This  action  is  often  strong 
enough  to  produce  a  pressure  in  the  radiator  lower 
than  atmospheric  pressure. 

The  vacuum  system  of  heating  in  which  the  air  is 
drawn  from  the  air  valves  is  particularly  desirable  in 
hospitals  and  school  buildings,  as  it  does  away  with 
the  objectionable  odor  from  the  air  valves.  This  vac- 
uum system  of  heating  does  away  very  largely  with 
the  attendance  required  by  air  valves. 

The  best  example  of  the  second  type  of  vacuum 

226 


Notes          on          Heating         and         Ventilation 

system  is  the  Warren  Webster.  This  consists  of  an 
automatic  outlet  valve  on  each  coil  and  radiator  con- 
nected to  a  return  system  in  which  vacuum  is  main- 
tained by  means  of  a  pump.  These  automatic  valves 
are  traps  which  allow  the  water  of  condensation  to 
pass  but  close  as  soon  as  the  water  is  removed. 

One  of  the  advantages  of  this  system  is  that  it 
permits  of  the  quantity  of  steam  entering  the  radiator 
to  be  regulated  without  any  possibility  of  water  ham- 
mer. 

This  system  always  requires  two  pipe  radiator  con- 
nections, but  has  the  advantage  that  the  return  piping 
may  be  made  smaller  than  in  a  gravity  return  system. 

The  vacuum  system  has  other  advantages.  It  also 
permits  of  the  radiator  being  placed  lower  than  the 
level  of  the  boiler  and  the  condensation  is  raised  from 
the  lower  level  by  means  of  the  vacuum  in  the  system. 
Oftentimes  this  enables  the  engineer  to  overcome  seri- 
ous difficulties  in  the  design  of  the  heating  plant. 
These  systems  can  be  profitably  installed  in  old  plants 
where  the  steam  mains  are  overtaxed,  owing  to  fre- 
quent additions  to  the  plant.  By  additions  of  the 
vacuum  system  these  old  mains  can  be  made  to  carry 
a  larger  weight  of  steam,  the  vacuum  system  permit- 
ting a  higher  velocity  of  steam  in  the  system  without 
increasing  the  back  pressure. 


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OCT    4    1932 

®OV  2* 

Iggp 

DEC   *6  1934 

ftr-^ 

1936 


DEC    7 


DEC    9  133,5 


NOV  2 
NOV 


NOV  281937 


22, 


DEC  21  193? 


DEC  8 
NOV  27 


3 


LD  21-50m-8,-32 


'':^,;:       a 


? 


/•?// 

241307 


